There is no complete explanation on this question. But we could follow some explanations in history and fill the missing links ourselves.
- The original character of 耐 is 耏.
- The original meaning is not related to 寸, and not "endure" either.
- 而 is a pictorial word about facial hairs.
說文, a dictionary written in 100 CE, has an entry about 耏, i.e. "耏,罪不至髡也。从而从彡。". A longer version is written in 說文解字注, "耏,罪不至髡也。从而从彡。耐,或从寸。諸法度字从寸。". This means 耐 is a variant form of 耏.
耏 is a penalty of removing one's hairs beside ears. It is lighter penalty than 髡, i.e. removing all hairs. The sentence "諸法度字从寸" indicates that later 耐 replaced 耏 for the meaning in laws. We might speculate that 寸 is a kind of measurement and further relates it to laws. 耐 finally wins the favourite form in the long history.
The meaning of "endure" is derivative. We could make a guess that one bearing this penalty must bear some kinds of humiliation. This might be the reason it derives the meanings of "bear, endure, resist and patient".