To miss one's footing (physically), to step off a safe place and nearly fall or slip.
階段で足を踏み外してしまい、あわててつかまった。
I missed my footing on the stairs and grabbed on in a panic.
暗くて段差に気づかず、踊り場で踏み外した。
It was dark and I didn't notice the step, so I missed my footing on the landing.
岩場で踏み外すと危ないから、慎重に歩こう。
Be careful walking on the rocks — it's dangerous to miss your footing.
Figuratively, to go off the right track; to stray from the correct path or proper conduct.
あの有名な選手は一度踏み外してしまい、復帰するのに時間がかかった。
That famous athlete once went off the rails and took time to make a comeback.
彼は一時的に踏み外したが、家族の支えで立ち直った。
He strayed for a while but recovered with his family's support.
若者が簡単に道を踏み外さないように、教育が重要だ。
Education is important so that young people don't easily go astray.