expression
sacrifice a small thing to save a great one; lose a leg to save one's life
A proverb advising that it is sometimes necessary to sacrifice something of lesser importance in order to preserve something of greater value. The literal image is of letting a large bug live while killing a small one.
大の虫を生かして小の虫を殺せというように、多少の犠牲はやむを得ないこともある。
As the proverb says, 'sacrifice a small thing to save a great one,' sometimes a certain amount of sacrifice is unavoidable.
The exact origin is uncertain, but it is a traditional Japanese proverb using the metaphor of insects to illustrate a pragmatic trade-off.