To expend a great deal of effort; to be strenuous or laborious.

Negative adverb used before verbs, adjectives, and other adverbs to indicate negation; also used as a bound-form prefix to form terms with opposite meanings

To get a desired outcome or have one's effort rewarded; used mostly in the negative to describe thankless tasks, such as in the phrase 费力不讨好 fèi​lì​bù​tǎo​hǎo.