Opinions on building a product for yourself vs. doing user research (personas, 5 whys method, understanding your target customer, etc.)?

It depends on how good you are at extracting useful data from your 'customer'. If you go wrong about finding his/her problem you could be f*cked because it might not be a real problem although he/she describes it to you as one.

On the other hand you are the expert of your own problem so you don't have to worry about the above.

I hate when people suggest books as I hardly ever read books but 'The Mom Test' is an amazing one where you can learn to validate your assumptions properly and learn truly if what people describe to you as a problem is really a problem. :)

i think the key weakness of lean methods of finding product market fit is that it extends the time to market and is very costly for bootsrapping companies. i speak from experience. so for me, i am hoping that the problems i have and the means i use to solve them, resonates with more people. and if one idea fails, i will not have spend a ton of time and money, so i can test another.