I'm familiar with lean methodology and aware that ideas don't really mean much, but at the same time I'd like to work on some big problem that's compelling. I know that I'll probably pivot a lot but just to start out what general problem would you reccomend I try and solve?
The problem you have, as is so common with many of these answers, is that they try to jump right to the problem. Wrong. It is like looking for a job. In reality you are looking for 100 places to send your resume to get 20 interviews to get 3 offers so you can pick one. So you need a methodology that puts lots of ideas in the hat and then you narrow it down through a funnel process. Marketing 101.. See Marketing Textbook from profs at Kellog School (NorthWestern).