Firstly, they are only 100 calories per bar.
Secondly, they taste like ass.
OK, it doesn't taste that bad, I mean they're no Sun Chips, but they aren't exactly good either. This makes them much easier to resist and also prevents me from going to the snack machine, after all I have a free snack right there! If I'm really, really hungry then at least it is only 100 calories and I won't be tempted to have more than 1.