Is it also a bias when the stocks I own seem better?

Yes. The endowment effect is the psychological phenomenon of valuing an item or asset more highly when you own it than when you do not, so that giving it up feels like a loss.

In investing, it can show up as magnifying the merits of the stocks you hold and putting off an objective reassessment. It helps to ask yourself whether you would buy the same asset if you were buying it fresh today.