What's the mental burden of trying to do something? What's it cost? What price are you going to pay if you try to do something out in the world?
I think that by figuring out what the usual costs to doing things are, we can reduce the costs and otherwise structure our lives so that it's easier to reach our goals.
When I sat down to identify cognitive costs, I found seven. There might be more. Let's get started -
Activation Energy - As covered in more detail in this post, starting an activity seems to take a larger of willpower and other resources than keeping going with it. Required activation energy can be adjusted over time - making something into a routine lowers the activation energy to do it. Things like having poorly defined next steps increases activation energy required to get started. This is a major hurdle for a lot of people in a lot of disciplines - just getting started.
Opportunity cost - We're all familiar with general opportunity cost. When you're doing one thing, you're not doing something else. You have limited time. But there also seems to be a cognitive cost to this - a natural second guessing of choices by taking one path and not another. This is the sort of thing covered by Barry Schwartz in his Paradox of Choice work (there's some faulty thought/omissions in PoC, but it's overall valuable). It's also why basically every significant military work ever has said you don't want to put the enemy in a position where their only way out is through you - Sun Tzu argued always leaving a way for the enemy to escape, which splits their focus and options. Hernan Cortes famously burned the boats behind him. When you're doing something, your mind is subtly aware and bothered by the other things you're not doing. This is a significant cost.