It's Monday! Have a profitable product? Share your problem validation steps in early days!

Hi. Do you have a profitable project (even $1)? Product Hunt has many not-yet-profitable hackers (like me). We (at least me) are happy to know your experiences in early days How did you identify "who" has "a problem"? What was your MVP that time? If you went back to those days, would you do the same things? or Do you know a better way now? Thanks,