From a broader perspective, bear in mind that the Trouble Aspect is there to help drive conflict (necessary for an interesting story). If things are slowing down at the table or you're struggling to find a direction for the story, grab one of the troubles and apply some pressure.
As a caveat, though, I'm going to emphasize what others have said about collaborative character building. If you have a Knight of the Cross and a Denarian in the same party, then something went wrong during character creation.
But also remember that the trouble aspect can also be an easy source of fate points for the player. For example, in my game I have a pair of twin changelings in my campaign who took the trouble, "Two sides of the same coin." In practice, I've used this to basically make them share consequences. "Oh, your brother has a broken ankle? Well, you're feeling his pain. How does a fate point sound for no mobility this round?"