While I agree with the author that engineers tend not to solve customer problems, but technical ones, what I was hoping he would get to is how to actually go about finding problems to solve in the first place.
In my personal journey, this has become the most difficult point in doing any sort of side project development. Sure, I can build prototypes, but for who? And why?
I think dogfooding (where applicable) and actually talking to other potential customers is most important. It helps in context of spending your resources to make more impactful improvements for your existing project (like building a cheaper dishwasher instead of a faster one).
With that in mind, it really helps to find your niche and converse with others in that niche. If you go to a niche forum like arcade museum or arcade projects, you might find people saying "I wish I had something to enable auto-fire on my arcade cab" and also people with the knowhow to build it and turns that into a product, or people having an interest check for a product they've developed for themselves to see if it has a wider audience.
In my personal journey, this has become the most difficult point in doing any sort of side project development. Sure, I can build prototypes, but for who? And why?