File:Blast through diagram.png

Summary
A diagram explaining the details about the blast through glitch.

On the top scenario, the character being knocked back is moving too slow, and as such, the difference between each position in each frame is rather short. It's not enough to cross the wall in a single frame, and a collision is seen being detected. In-game, that would make the character bounce back.

On the bottom scenario, the knockback is strong enough to let the character pass through.