It was a slippery slope.

Meaning

A situation or course of action that, once begun, is difficult to stop and leads to something bad.

Examples

• John: I should have stopped earlier.
• Alice: Yes, <b>it was a slippery slope</b>.
• John: I know. I learned my lesson.
• Alice: It's good you recognize it. <b>It was a slippery slope</b> you were on.