The life inside your head eventually starts negotiating the life outside of it.

The conversation you run privately sets the terms for what you are willing to accept publicly. If you have spent years telling yourself you are difficult to love or not worth much, you will negotiate accordingly, and you will call the result realism. Nothing dramatic has to happen for this to work. The inner story simply keeps setting the opening offer.

Notice where you accept less than you would want for someone you care about. Ask what you must be assuming about yourself for that to feel appropriate. Changing the assumption is slow, but even naming it changes what you agree to next time.