Three tails that clamp behind a stative verb to push its degree to the extreme.
框 · Frame
[Vs] 極了 / [Vs] 得不得了 / [Vs] 得很
觸 · Trigger
The adjective alone is too weak; you want to push it to the extreme, and the booster goes behind it.
序 · The move
1state the stative verb (the quality) bareis this an adjective/feeling, not an action verb?
2pick a tail and clamp it on the end: 極了, or 得不得了, or 得很does the booster sit after the adjective, with nothing pushed in front of it?
3leave no front booster (no 很, no 非常) when a tail is used是 高興極了, not 很高興極了 — front and tail not both firing?
例 · Examples
1他終於買到演唱會的門票，心裡高興極了happy, topped out — extremely happy。這間店的空間雖然不大，但是每天生意都好得不得了good past what can be got past — incredibly good。這個香蕉蛋糕的作法簡單得很simple, fierce degree — dead simple。
He finally got the concert ticket, and inside he was overjoyed. This shop is small, but business every day is incredibly good. This banana cake is dead simple to make.
很 + Vs puts the booster in front (很高興); these three put it behind (高興極了, 高興得不得了). Front slot is the everyday degree; tail slot is the extreme. Run them backwards and they break: 極了高興 and 不得了高興 are not Chinese.
V 得 + 補語 hangs a verdict behind an action — how it went (跑得很快 = ran fast). 得不得了 / 得很 hang behind a quality and boost it (好得不得了 = good to the extreme). Action getting rated vs. adjective getting maxed out.
front booster on the tail form: 很高興極了 → 高興極了
tail on an action verb: 他跑極了 → 他跑得很快 (action takes a verdict, not an extreme tail)
dropping 得 before the boost: 好不得了 → 好得不得了
English stacks the intensifier in front of the adjective (extremely happy, incredibly good); learners reach for 很/非常 up front and never let the booster ride behind the quality.