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I just got back from the July CFAR workshop, where I was a guest instructor. One useful piece of rationality I started paying more attention to as a result of the workshop is the idea of useful questions to ask in various situations, particularly because I had been introduced to a new one:

"What skill am I actually training?"

This is a question that can be asked whenever you're practicing something, but more generally it can also be asked whenever you're doing something you do frequently, and it can help you notice when you're practicing a skill you weren't intending to train. Some examples of when to use this question:

• You practice a piece of music so quickly that you consistently make mistakes. What skill are you actually training? How to play with mistakes.
• You teach students math by putting them in a classroom and having them take notes while a lecturer talks about math. What skill are you actually training? How to take notes. 
• A personal example: at the workshop, I noticed that I was more apprehensive about the idea of singing in public than I had previously thought I was. After walking outside and actually singing in public for a little, I had a hypothesis about why: for the past several years, I've been singing in public when I don't think anyone is around but stopping when I saw people because I didn't want to bother them. What skill was I actually training by doing that? How to not sing around people. 

Many of the lessons of the sequences can also be packaged as useful questions, like "what do I believe and why do I believe it?" and "what would I expect to see if this were true?" 

I'd like to invite people to post other examples of useful questions in the comments, hopefully together with an explanation of why they're useful and some examples of when to use them. As usual, one useful question per comment for voting purposes.