expression, ichidan verb
be extremely cautious; make doubly sure
Idiomatic expression meaning to take every possible precaution, double-check everything, or leave nothing to chance.
大事な書類だから、念には念を入れてコピーを取っておいた。
Because it's an important document, I made doubly sure and made a copy.
旅行の前には、念には念を入れてパスポートの有効期限を確認する。
Before a trip, I check my passport expiration date with extreme caution.