expression
in wine there is truth; drunken words are sober thoughts
A proverb meaning that a person's true nature is revealed when they are drunk; alcohol does not change one's fundamental character.
彼は酔うと急に優しくなる。生酔い本性違わずだね。
He suddenly becomes kind when he's drunk. It's true that in wine there is truth.
生酔い本性違わずというから、あの人の本音はああなんだろう。
As they say, drunken words are sober thoughts, so that must be what he really thinks.
A similar proverb meaning 'sake reveals the true heart'; more direct and less classical in wording than 生酔い本性違わず.
A classical Japanese proverb. The exact origin is uncertain, but it reflects a long-standing folk belief that intoxication reveals one's true nature.