“Above all, it is necessary for a person to have a true self-estimate, for we commonly think we can do more than we really can.”
Seneca, On Tranquility.

What happens when you see yourself as more capable than you really are, and then you are unable to achieve what you believed you could? How does that feel? Or what if you held yourself back from attempting something because you judged yourself to be incapable of it? What emotions do you get then?

If you never try something, you’ll never find out. Better to try and make best use of the feedback – in the here and now – than to live in continual self-delusion.