It seems to me that the more you have a propensity to think (or over-think), the more likely it is that you may be able to construct rationalizations (excuses) before/during the moment as to why you might not be able to do something. More insidiously, you can construct these excuses after the moment passes, like an endless negative Nancy TiVo gone berzerk in your mind.
There is no one-size-fits all solution to self-doubt, lack of confidence, etc. Really, the only solution for nagging self-doubt is to generate contradictory evidence to self-doubt. That is, do something.
Motivation is not ideal either because usually it makes you think you can do something.
The more I work on meditation and visualization and other techniques - the more aware I am in the actual moment of when I am resisting doing something out of my comfort/risk zone. There is a lot to be said for Zen and Stoicism, as well. And in the end, only you (or your closest friends or partner) know when you are not pushing yourself.
> ... I am resisting doing something out of my comfort/risk zone.
Interestingly, we resist because we perceive a loss of options or in other words - freedom, caused by the paralyzing anxiety. We usually feel free by being in our optimized space, where we have already invested a lot.
And the purpose of going out of out comfort zone is exactly the same - to maximize freedom or diversity of options. By embracing novelty, new options might be discovered and more freedom acquired.
It's the classic trafeoff between exploration and exploitation. Both exploration and exploitation are necessary to maximize results, and the balance between them is not a trivial issue. Always going out of your comfort zone can do as much harm as always avoiding novelty.
By the way, Reinforcement learning algorithms such as AlphaGo deal with the same issue. The simplest solution is to follow the optimized policy ("be in the comfort zone"), but from time to time to do random exploration steps in order to discover more of the state space and possibly find better strategies. In the beginning of the training sequence, it's more exploration, but later, more exploitation.
While there are some things that I am very good at naturally, there are many things (especially in the social sphere) that I struggle with. The problem is that I've developed camouflage that makes my acquaintances and even some of my friends think that I am better in some of these areas than I know that I am.
Having bought (and eventually given most away) pounds and pounds of self-help/self-improvement books over many years, there are common patterns in each book. They are all marketing to fix X problem with Y techniques. All parts of every technique Y may not work for you. However, like agile/scrum, there are parts of it that may be worth using for you, personally.
Having someone that knows you help keep you accountable (even better if you are both keeping each other accountable - or a small group) may work for you. You can also hire a personal coach. The accountability doesn't have to be every day (that is micromanagement and would get exhausting on both sides). Something like once or twice a month can work well. A regular 8am meeting twice a month, for example. It doesn't have to be face to face, it can be over Skype.
Finally, you may encounter the strongest resistance from yourself. Simple stuff like going to a yoga class instead of, say, a tech meetup. Or trying to meditate or visualize every day (the key tip here is do it before you turn on your laptop or your phone - do it right away, in the morning, as you roll out of bed). Saying hi to that cute person or not - and regretting it until it fades. You can make excuses until "the cows come home". And in the end, just doing it is what matters.
There is no one-size-fits all solution to self-doubt, lack of confidence, etc. Really, the only solution for nagging self-doubt is to generate contradictory evidence to self-doubt. That is, do something.
Motivation is not ideal either because usually it makes you think you can do something.
The more I work on meditation and visualization and other techniques - the more aware I am in the actual moment of when I am resisting doing something out of my comfort/risk zone. There is a lot to be said for Zen and Stoicism, as well. And in the end, only you (or your closest friends or partner) know when you are not pushing yourself.