The scariest thing in all of climbing is falling. And perhaps the hardest thing to do in all of climbing is to manage the fear of falling. The Clip-Drop technique is a way to train your brain to accept that falling is a part of the game and that in many cases, that falling is perfectly safe.
In a nut-shell, the Clip-Drop technique is simply what it says. You clip a bolt, climb up a bit and fall. You clip the next bolt, climb up a bit and fall again. The idea is that if you do this all the way up a route, you will become accustomed to falling and will be able to get past the fear of it.