A failure or blunder; an error or mistake (often used colloquially to refer to having messed something up).
試験でしくじり、来年もう一度受けることになった。
I failed the exam and now have to take it again next year.
彼のしくじりが原因でプロジェクト全体が遅れた。
His blunder caused the entire project to be delayed.
小さなしくじりならあまり気にしないでいいよ。
Don't worry too much about a small mistake.