Four characters, one worldview
Chengyu 成语 are usually four characters and almost always mean more than their parts. Read them literally first — the gap between literal and real is where they live.
画蛇添足 · Draw a snake, add feet
A man finished drawing a snake first and, with time to spare, decided to improve it with legs. He lost the prize. To ruin something by adding what it didn't need.
The English cousin: gilding the lily.
塞翁失马 · The old man at the frontier lost his horse
The horse ran off; neighbours commiserated. It returned with better horses; neighbours congratulated. His son broke his leg riding one; they commiserated again — and the injury kept him from conscription. Bad luck, good luck, who knows.
A blessing in disguise — and more precisely, reserve judgement.
饮水思源 · When you drink water, remember the source
Don't forget where you came from, or who made it possible. Applied to teachers, parents, homeland.
Less poetic than it sounds in Chinese — this one gets used seriously.
入乡随俗 · Enter the village, follow its customs
When in Rome. The Chinese version is more literal and slightly less resigned about it — the advice is to adapt as a courtesy, not merely to survive.
Useful to know before your first Chinese business dinner.