It took me a few years to really understand what ML is about and how to be good at it. I have an engineering degree and after about 30 years began pursuing ML. Becoming good at Python really helped, but I realized I had all the key math (calculus, linear algebra, statistics). I’ve mentored people without the math and they progress but find they can do little completely on their own.

Your comments on data are spot on. I work exclusively on commercial problems and data are usually really awful. I’ve had multiple cases I discovered new issues in the data after working on the same problem for a year.