Plot Structure

I'm deep in revisions for my WIP (okay, I'm procrastinating and blogging) so I've been thinking a lot of deep thoughts about plot. What the heck is it? What holds it together? In Plot and Structure James Scott Bell addresses some of these same questions. He advocates using the Three-Act Structure. He phrases it in terms of Mythic Structure/The Hero's Journey. The crucial ideas here are a disturbance and two doorways. A novel begins with character in ordinary world, then early in the novel a disturbance occurs. Then the Lead must be thrust into the main conflict (Act II/Middle) in a way that keeps him there through the first doorway. Finally, to move from the middle to the End/Act III―the second doorway of no return―something has to happen that sets up the final confrontation.

Many of you (and I) have seen these ideas before but they're important. Something must happen to thrust the protagonist through the first doorway SO HE CAN'T GO BACK. If the protag can just shrug, say "Nah.", and go back to his ordinary life the author hasn't done his/her job. Similarly, the second doorway must also be a point of no return.

Tricky. Did I do this in my WIP? I better go back and analyze some more.

How about you? Any tips or tricks for creating points of no return? Thanks!