unintentionally; without meaning to; against one's better judgment
Expresses doing something one knows one shouldn't, often due to habit or weakness. Similar to つい but with a stronger sense of self-reproach or repeated failure.
See also: つい
Even though I'm on a diet, I ended up eating without meaning to.
Even though I'm on a diet, I end up eating sweets without meaning to.
仕事中についついスマホを見てしまう。
I find myself unconsciously checking my phone during work.
セール中だと、ついつい要らないものを買ってしまう。
During sales, I end up buying things I don't need without meaning to.
Reduplication of つい, an adverb of spontaneous or careless action. The exact origin of つい is uncertain, but the reduplicated form intensifies the sense of repeated, involuntary behavior.