吃一堑 is the first half of the common saying 吃一堑，长一智 (chī yī qiàn, zhǎng yī zhì), which means 'a fall into a pit, a gain in your wit' — you learn from your mistakes. By itself, it means 'to suffer a setback' or 'to experience a failure'. This is a fixed verb-object expression; you cannot separate or modify the syllables (e.g., do not say 吃了一堑 as a separable verb). The phrase is used to encourage learning from adversity.