It didn't work? I do it again!!!

[Oriande]

So…  Two player characters encounter an unknown threat and engage in combat.  The opponent appears able to shrug off their initial attacks.  One player then begins to vary his approach while still relying on the same ability. The other, proceeds to repeat the same action, over and over, evidently convinced that all he needs is the right roll and grows frustrated when this is not met with success.   What should I do? 
I don’t want to stop the game to suggest that he try something else.  There is a lot of tension at this point and the other players are all caught up in the action.  Also, I don’t really feel that I should have to explain the opponent’s abilities and defenses.  I want the PC’s to figure them out on their own.   

[deathwombat]

Let it eat his face
Do your descriptions  make it clear the PC  is ineffective?

[Tedronai]

inflict a consequence on each of them, then use those consequences to compel them to realize that this is a losing battle, and that they need to book it out of there
allow them to concede (they're battered and bruised, maybe toss in an extra consequence if they you think they're getting off easy, but they manage to escape), give them each a fate point for any consequences they took in that fight past the ones you just compelled (don't give them a fate point for the same consequence twice, since you're basically just paying them in advance with this whole compel to concede scheme)

[Marganma]

If the player just doesn´t know the rules well enough to know that his move is futile, you should let him know.

If he does (or should, because you´ve been playing DF long enough) and just doesn´t want to try and think up another move, then it´s his funeral.

[zenten]

Make sure to let the second player know that no stress is being dealt.

[UmbraLux]

So…  Two player characters encounter an unknown threat and engage in combat.  The opponent appears able to shrug off their initial attacks.  One player then begins to vary his approach while still relying on the same ability. The other, proceeds to repeat the same action, over and over, evidently convinced that all he needs is the right roll and grows frustrated when this is not met with success.   What should I do?  
I don’t want to stop the game to suggest that he try something else.  There is a lot of tension at this point and the other players are all caught up in the action.  Also, I don’t really feel that I should have to explain the opponent’s abilities and defenses.  I want the PC’s to figure them out on their own.  

Work on your descriptions.  "You land a perfect strike to the neck but your sword scrapes ineffectively across the armored scales." is more to the point than "No damage, next!".  Basically you want to make two things obvious, 1) it was a great blow that would have severely hurt lesser foes and 2) it was so ineffective the guy doesn't even consider him a threat.  Having one use an obviously invokeable Maneuver like "Concentrating on <effective guy>" can make the point even blunter...while setting up a bonus!  

[Oriande]

Work on your descriptions.  "You land a perfect strike to the neck but your sword scrapes ineffectively across the armored scales." is more to the point than "No damage, next!".

Actually, as the persistent attacks were all gun shots it was more of "Alright, you hit him square in the torso. He rocks back about half a pace and you see his head turn in your direction."  which led to three more rounds (no pun intended) of ineffective gunfire.

Meanwhile, the Focused Practitioner, having failed to produce much reaction from a six shift blast of wind, decided to change his tactics.  He aimed his next shot at the side of the path and angled it to kick up dust and debris.  This bought them a round free of retaliation and another bit of information as they saw a snake-like tongue flicker out to clear his/its eyes. 

This player then proceeded to grab a handful of sharp pebbles etc. and launch them directly at the nearer eye.  After that, he aimed a telekinetic burst, not at the opponent, but at the structure next to him  -- a sort of Wicked Witch of the West solution; although he did not drop an entire house on it – just a decorative wooden beam and some plaster.   
And all this time, the other player continued to empty a clip. One of us is definitely missing something. 

[zenten]

Usually when players do stuff like that it's because they just can't think of anything else to do.

[Haru]

Usually when players do stuff like that it's because they just can't think of anything else to do.

Pretty much what I was thinking.

You could try and create some sort of "mortal spellbook" with him, effectively giving him some ideas of what to do with his skills and stunts. Maybe if he gets started in the right direction he will start to think of unusual things himself. Don't do it ingame, take half an hour before you play, maybe let every player contribute, and you are going to have a whole lot of maneuvers to do for him, so he will have a better understanding of what his character is capable of. Especially explain the power of maneuvers to him, because that is something most players seem to neglect when they want to take something down.

Once you are in a scene like that, depending on the opponent, he might make a comment like "Your tiny weapons are nothing to me, ape.", telling him very clearly, that a different approach might be better suited in this situation.

[UmbraLux]

Actually, as the persistent attacks were all gun shots it was more of "Alright, you hit him square in the torso. He rocks back about half a pace and you see his head turn in your direction."  which led to three more rounds (no pun intended) of ineffective gunfire.

<snip>

And all this time, the other player continued to empty a clip. One of us is definitely missing something. 

Your description sounds good, but may not be obvious enough for someone fixated on using his primary / normal attack.  I'd suggest something along the lines of "You hit him square in the torso opening gaping wounds...which immediately close as if nothing harmed him." or equivalent.  Sometimes you simply have to make it inescapably obvious that repeating the same action won't have a different effect.  

We all tend to have moments of 'solution lock' - where we've decided the solution already and find it difficult to react creatively.  That may bring up another point - how often has this character had to solve problems with something other than a gun?  Perhaps he simply needs to break the 'shoot first' habit...

[Tedronai]

Your description sounds good, but may not be obvious enough for someone fixated on using his primary / normal attack.  I'd suggest something along the lines of "You hit him square in the torso opening gaping wounds...which immediately close as if nothing harmed him." or equivalent.

Might try a page straight from Superman Returns, and have one of those bullets hit the big bad straight in the eye and bounce right off, if you want to really drive it home.

[Belial666]

The problem with guns is that, if your opponent is immune to the damage they deal, it is really hard to justify other actions with them; OK, you want to block and lay down suppression fire. Now, why would the bullet-immune enemy bother to take cover at all?

[UmbraLux]

An autofire based block won't work against a bullet-immune foe.  The book points that out using the Loup Garou as an example.  There are still a few maneuvers you can do - anything indirect.  Fire at the floor to cause 'Unsure Footing', at the lights to cause 'Darkness', at cleaning supplies for a 'Slippery Floor', etc.

Even so, there are times it may be better to put the gun aside and do something else.  One more argument against overly specialized characters.

[noclue]

Actually, as the persistent attacks were all gun shots it was more of "Alright, you hit him square in the torso. He rocks back about half a pace and you see his head turn in your direction."  which led to three more rounds (no pun intended) of ineffective gunfire.

And all this time, the other player continued to empty a clip. One of us is definitely missing something. 

Don't call for a dice roll if the gun is inneffective. Just narrate him emptying his entire clip into the thing without result. Then I would have asked "What do you do now?" and let him make whatever action he wanted to try at that point.

[sinker]

Agreed. This is something I think not a lot of GMs think about, but it helps keep the pace quick and really does make things clear to the players. If the consequences of the action will not change, regardless of how well or how poorly it's done (in this case, he will hit it and draw it's attention with no other effect, or he'll miss and draw it's attention with no other effect) then there's no real reason to have them roll. Just narrate it and move on. Then you don't have the player trying for the perfect roll, because you've made it clear that there is no practical difference between a -4 and a +4.