This means something is the best choice. It is the safest or most helpful option. Other choices are not as good.
Verb [dictionary form] + にこしたことはないPrimary
い-Adjective + にこしたことはない
な-Adjective + にこしたことはない
Noun + にこしたことはない
This means something is the best choice. It is the safest or most helpful option. Other choices are not as good.
用心するにこしたことはない。
You can't be too careful. (lit. There is nothing better than being cautious.)
家賃は安いにこしたことはないよ。
When it comes to rent, the cheaper the better, you know.
借金はないにこしたことはない。
It's best not to have any debt.
旅行は直行便にこしたことはないが、乗り継ぎでも安ければ構わない。
A direct flight is best for travel, but I don't mind a connecting flight if it's cheaper.
あの時、正直に話すにこしたことはなかったと、今になって後悔している。
I now regret that it would have been best to speak honestly at that time.
This phrase says one choice is the very best. It is like saying, "This is the safest path." But it does not mean other choices are bad. It is a strong suggestion, not a rule. You might still pick something else.
This is like '〜に限る' (ni kagiru). But '〜にこしたことはない' is general advice. It is about what is safest or best for anyone. '〜に限る' is about what you like best. It is your personal choice.
Don't use this when you are speaking politely. For example, saying "安いですにこしたことはない" is wrong. You can use a past tense, but it is rare.
More formal alternatives(1)
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