What is hook?
The most memorable part of a song — often the title line, sung at the point the listener is most likely to remember it. Hooks are usually short, repeated, and built from plain, concrete language.
A hook that needs explaining is not a hook yet. If a first-time listener cannot sing it back after one pass, the problem is normally length or abstraction.
The match between the natural stress of spoken words and the stresses of the melody. Good prosody makes a lyric feel inevitable; bad prosody makes a singer fight the line even when every syllable technically fits.
The melody and lyrics written over an existing instrumental. Topline writers work fast against a finished track, which is exactly the situation where memorising a brand-new lyric is unrealistic.