"Because who will put up with you if you don't even think you're worthy of love."

The answer is people who don't know the real you. Would anyone love you if they saw a clip show of all the lies, betrayal, hypocrisy, times you yelled at your family, embarrassing fails, wasted potential, etc. But for many of us that clip show plays daily in our heads as a reminder to stop being so shitty and it comes at the price of our self-esteem.