Midlife dissatisfaction seems to be a natural and normal transition, as our values change and our brains develop.

中年的不满足似乎是一种自然的、正常的转变，因为我们的价值观变了，我们的大脑发育了。

" Variable" means changing;the value changes over time.

“可变”意味着变化；值随时间而变化。