Rationalization offers a plausible-sounding justification for behavior that is actually harmful or excessive, and it works precisely because the justification is plausible — not obviously false, just incomplete. "I push my daughter hard because I want her to succeed in a competitive world" sounds like ordinary parental concern, which is exactly what makes it effective at deflecting an otherwise legitimate objection. George Simon's clinical observation is that the plausibility itself is the trap: the listener starts arguing about whether the justification is reasonable, instead of evaluating whether the underlying behavior is actually harmful.
The practical fix Simon offers is a reframe: don't debate the excuse on its merits at all. A justification, however reasonable-sounding, doesn't change whether the behavior itself is causing real harm — the two questions are separate, and manipulation specifically works by merging them into one.