Does telling someone "he is fixated on something" have a negative or positive connotation or it depends on the context? for example,
You are very fixated on your own research.
It depends on context. For example:
You are very fixated on your own research, but you need to work on the group project too.
In this case it would be considered negative or at least distracting.
You are very fixated on your own research, which demonstrates your willingness to succeed.
would be considered positive.
It depends on the focus (a good synonym) and the reason behind it.