不/沒（有）…，就…grammar point · tier 2 · negative condition 不/沒（有）…就… (without doing A, then B fails to follow)
Negative condition: A is left undone or absent, and then the consequence fails to follow.
字源 FORM what the parts do
不 withholds a still-undone action; 沒（有） withholds one that never happened; 就 fires what follows from the gap. The consequence after 就 usually carries its own negation (不會、無法), so the missing step shuts the result down.
故事 STORY a scene to remember it by
A key lies beside the lock, never turned; behind the door it would have opened, the latch holds and the room stays sealed. Leave the turn out and nothing past the door moves; the door does not swing open on its own.
自撰字源記憶法
框 · Frame
[subj] 不/沒（有） [withheld action]，[subj] 就 [consequence, usually 不會/無法/沒辦法 …]
觸 · Trigger
You warn that skipping one step leaves the result out of reach.
序 · The move
1Open the condition with 不 for a withheld action or 沒（有） for one that did not happen.不 negates will or a not-yet-done act; 沒（有） negates a completed one. Pick by which the missing step is.
2Open the consequence clause with 就 before its verb.Does 就 sit right after the subject and before the verb of the consequence?
3Give the consequence its own negation (不會、無法、沒辦法) so the missing step blocks the result.Read it as 'no A, so no B'. If B still happens without A, this frame is the wrong one.
例 · Examples
1沒有did not / without (having)填寫fill in信箱email box，申請application就then不會won't成功succeed。
If you don't fill in your email, the application won't go through.
如果…就… names a condition either way; 不/沒（有）…就… fixes the condition as the absence of a step, and the consequence is what then fails to follow.
只要…就…
只要…就… says one thing is enough to bring the result (do A, get B); 不/沒（有）…就… says skipping that thing keeps the result away (no A, no B). The two are the same gate read from opposite sides.