Practise the thinking. Keep the judgement.
もったいない — Wasteful; too valuable to waste
もったいない
mottainai
Meaning
Wasteful; too valuable to waste
Original example
まだ使える物を捨てるのはもったいないです。
Throwing away something still usable would be wasteful.
Cultural context and nuance
Regret at wasting usefulness, value or opportunity. Also used when something feels more generous than one deserves.