"If you're solving a real problem people will not have an issue paying you"
The counter to this is you don't know at the outset:
- whether you have identified a real problem
- whether you are solving the problem the right way
- whether the amount the buyers are willing to pay aligns with how much you need to earn for solving the problem
- how many actual (vs potential) buyers there are for a solution to this problem
- how difficult (read: expensive) it is to find people with this problem and make them aware of your solution
- how quickly a better-funded company will come in and offer a better (in some way) alternative
- how much you like (dislike) working with the median purchaser of your solution
- how much enjoyment you personally derive from providing this solution
- etc.
All of these lead to the realization that it might be possible to struggle it out with a given niche, but it might not be the best course of action for you personally.