So I encountered this sentence in a manga
泣きたい日もあるじゃない
and I thought it was weird but meant something along the lines of "I never feel like crying", because of the negation of 泣きたい日もある, which I understand as "There's (also) some days when I/you want to cry" (of course I'm imposing the first person pronoun, but you can change it accordingly).
Just to check, I looked up the translation of the manga, as well as used deepl.com and they both translate this sentence as "Some days you just want to cry", which is the opposite of what I thought at first!
I looked parts of the sentence up thinking this may be a usual grammar point but can't find anything. Could someone explain what's going on?