Once in a while you should cut your players a little slack. If a roll is within one of accomplishing a feat, you might just want to give it to him/her. In taking down stormtroopers, the difference between wounded and incapacitated is nothing. They're losers. They fall down if they get hit once. If somebody tries to break down a wooden door and almost reaches the difficulty level, just call it good. They busted through. Maybe, say, awkwardly and they fall on the floor with the door. But give it to him/her anyway. If it's something they're just going to try over and over again and it'll take forever to do, just adjust the difficulty level to include a couple under. You might really want them to accomplish something and if they're close, let 'em have it. This saves time, energy, patience, and keeps the enthusiasm up. And the killer--they don't even have to know. They feel excited, maybe relieved, at their accomplishments and game can go on.