"pushing" a roll

Sometimes a failure is not a big deal. If you miss while shooting arrow, nothing is stopping you from firing a second arrow next round at the same difficulty.
Sometimes failure is a very big deal and you can't redo anything. If a gemcutter is cutting a diamond, and she messes up, you cannot undo that.
Other times a failure is a serious setback, but is not irredeemable. In this case you can push a roll and try to undo a failure or push up a marginal (one success roll).
To push a roll, the player spends a temporary Willpower point and tries again with a slightly different approach.
The player needs to come up with a different approach that is feasible. For instance, if you tried to solcit a mercenary to join your cause with gold, to push the roll, you need to offer substantially more gold or try appealing to his honor or pride instead of his greed.
If you cannot pick a lock with some wire in the key hole, maybe you can pry it apart with a fulcrum of some sort.
Sometimes, a different character can push the roll. If Player A fails a social roll, Player B can step in and explain "What my companion meant to say was..."
No matter what alternate approach the PCs take to push a roll, the difficulty for the second roll goes up by +1.
In most cases, a botched roll cannot be pushed unless the player has a really great idea for an alternate approach.