An identity crisis is when one's self-concept starts to change drastically or conflict with the existing self-concept. I think it has more to do with a major shift rather than "small" changes. Drastic changes would cause one to become anxious & stressed due to the conflict. It is the accompanying stress that makes it a crisis.

Example: I am a very kind, sweet person. But now I want to maim & hurt others just for the fun of it. I would start to question who I think I am, why I'm changing, why I used to think of myself in such a way, why I want to engage in the new behavior, etc. Worse, I might deny myself the new urges or superficially overdo the old ones rather than address the change itself.

Not being able to "fit in" anyplace.

For example, many kids rebel against their parents but conform to the values of their peers.

But some kids identify with neither their peers nor their parents, and are uncomfortable conforming to the standards of either group.

Growing up without traditions of any sort may be another factor.
My ancestors came to this country as immigrants, but within a generation or two, any sense of cultural identification with the "old country" - or with the experience of the immigrant generation itself - has been lost.

An identity crisis is the result of desire frustrated by an unknowable reality.