At The Knowledge Project 169, Dr. Julie Gurner says to Shane Parrish: 

I think that there is a very strong link—more than we think—with hesitancy and self-esteem. For example, I think the more you hesitate, you see other people doing things. You watch, right?

If you don’t take the chance, and you watch other people taking the chances and doing well, now you’re one step behind. Then you watch them continue to take chances, now you’re three steps behind. Over the course of a year, you’re watching someone blow up and do great, and you know that person well, like, ‘Man, that guy’s doing it, and here I am still thinking about that idea I had and I didn’t do it.’ 

It’s an erosion of confidence, just over, and over, and over again, that hesitancy. So I do think that even if that bias to action, and the ability of people to make those moves as you said, you watch them do it and they do it over, and over, and over again, they know they can figure it out because the first leap—just taking that leap is like a shot in the arm, and it makes you feel a little bit more confident because you made that leap. Nothing went wrong, and now you can figure out, ‘Can you do the next one? Can you figure out the next step?’ 

Confidence stacks as you begin to continue to take risks, but I also think that hesitancy pulls you into this kind of negative loop, where it builds on itself too. You really have to be cautious that things don’t sit on the table, and you just look at them as you come in and out, because that will keep happening, and you’ll keep looking at it and it will keep bothering you.

Eventually, you just feel like—you’ll make up some rationalization why it didn’t happen like “Ah, I’m so glad I didn’t do that because I didn’t really have the time,” or, “I got to spend a lot of extra time doing this,” or whatever it is, but you’ll find a reason to rationalize it, and eventually it will go to the place where dreams die. There will be a lot of other things that will sit in that bucket with it. It will be unfortunate for you, because you never got to see what would happen.

The mental imagery of confidence (see also Dr. Nate Zinsser on making deposits into your mental bank account) and hesitancy compounding aligns with Gurner’s overarching theme of virtuous and vicious cycles. 

Anything we do, every day, can be considered a deposit into one of these areas. As I wrote for Lifehacker, it’s important to deliberately feed the thoughts you want to feed.

https://youtu.be/C5D6HAskUaE?t=2431
See also bias for action (and the prequel).