To get into a deep mess or trouble from which one cannot easily escape; a colloquial (somewhat coarse) expression for being stuck in serious trouble.
彼は投資で大損してドツボにはまってしまった。
He lost heavily on investments and ended up in a deep hole.
プロジェクトが遅延して追加費用が膨らみ、チームはドツボにはまった。
The project was delayed and extra costs ballooned — the team found itself in deep trouble.
ミスが重なって上司との関係も悪化し、彼は完全にドツボにはまっている。
Mistakes piled up and his relationship with his boss worsened — he's totally in a hole.