When you boast you have a choice.... you can play a two wall boast which strikes the side wall, then the front wall and then bounces on the floor. Or you can play a three wall boast which hits the side wall, the front wall and then the opposite side wall before it hits the floor.
Three wall boasts are a bit more risky because as they come round they are going to hit the front wall then the side wall, hopefully fairly low, but if we get it slightly wrong the ball is going to hit the side wall and come back out towards the middle. It is a higher risk shot but of course greater reward because if you get it nice and low down here you have a good chance of hitting a nick and hitting an outright winner.
Two wall boasts on the other hand are your percentage play. The ball is going to hit the front wall and is going to bounce and the ball is going to be hitable right in the side wall corner so you are pulling your opponent right off the 'T'.
So remember when you play your boast make sure you know whether you are trying to hit a two wall boast which will hit the front wall and then die close into the side wall....or a three wall boast which will hopefully nick out.