This is the 315th most frequent Japanese word.
つい
"Unintentionally" or "inadvertently."
Here, 'つい' emphasizes brevity of time, meaning 'just' or 'a moment ago'.
ついさっき彼に会いました。
I just met him a moment ago.
Here, 'つい' again reflects an unintended or accidental action, suggesting it happens by mistake.
つい忘れてしまうことがあります。
I sometimes accidentally forget it.
In this sentence, 'つい' expresses an unintended action, such as doing something without thinking.