I believe stropping is pretty easy, but like honing, I can't see whats going on. I think the idea is to apply a little bit of pressure to align the edge and build out the fin slightly to create two smooth bevel sides and an extended fin with which to shave.

If you imagine pulling a rope through water that would be like stropping a blade initially, thus no draw. If you imagine a ball tied to the same rope being pulled through water you'd get draw or pull on the rope. I think this is similar to what we get after some stropping. The fin is created a little on both sides and perhaps creates a similar "ball" on the edge, thus heavy draw.

Now, if you can imagine developing that fin, or extension and you either:

fail to allow the blade to pivot in your hand correctly while stropping, or go down too far on the strop with thumb pressure (or finger pressure), the fin will easily snap off.

You can easily imagine this if you know there is a fin extended out from your edge. Maybe this is why they say in barbers manuals you should hold the razor like a pencil your turning, it wouldn't be as likely to apply too much pressure while turning it.

And you can also see why its important to lessen the pressure as you go and to use a light touch at the end.

So I think the fin breaking is occuring typically not from too much pressure but from too much pressure, applied too far down the strop where the torque is being built up, which might explain why some videos show a slap straight down, a push off, and then lifting the blade off the strop instead of going the full length of the strop.

Perhaps also you can imagine how even light pressure would build up against the razors edge the further you push the razor down the strop and away from you body. This would, in some cases, cause the razors edge to break or roll, especially if you've built out your fin with previous stropping and fail to allow the razor to pivot in your fingers as you go.

Thoughts?