showing a lack of wisdom or judgement
naive - gullible
A person described as ‘naive’ is considered to be overly trusting of people and to mistakenly believe that life is more simple and fair than it really is. Often that is because the person in question is young and therefore without much experience of the world, rather than simply being foolish.
It was a little naive of you to think that Alex wouldn’t try to steal your idea. You should have kept it to yourself.
I rejected that job offer because, naively, I thought my boss would give me a promotion if I stayed. I wish I hadn’t now.
She was paying way too much rent for that place. It was the first time she'd lived away from home and the landlord was exploiting her naivete.