The role to resist and the roll to close the Sight are the same role. If you fail you are unable to close it and must spend the next exchange trying to resist/close it again.
But the Lore roll is an "assesment" action and if that fails, you get no information and therefore could keep your Sight open another exchange to attempt another assessment action. The Lore roll is the same difficulty as the intensity. So an intensity 5 vision is a Lore 5 to discover anything useful. With that in mind, if his Lore is lower than his discipline, he might need to keep his Sight open for multiple rounds, giving him more opportunities to fail his discipline.
EDIT: I'd also like to add that, according to YS, looking at Murphy - because she's a main character, central to the plot etc... - was a +4 Great difficulty to resist. Seeing the cop wracked by the psychic vine was +3.
It also advises that all visions START at +3. THis can go up or down depending on whether the wizard focuses on something small (gets less information) or focuses on the larger picture (gets more information). It doesn't say so, but I imagine the difficulty of the lore roll would go up or down in proportion of how focused the wizard is trying to be.
With that said, if your player has a lower Lore, you can tell him he'll have an easier time deciphering the Sight if he takes in more information. This is a "by the rules" way of increasing the difficulty to resist.
