Work at a B2B services firm for a while. You'll get exposure to hundreds of businesses over a few years.

I've seen industry outsiders solve a nonexistent problem, or fail to solve an existing problem without realizing it, or solve a non-generalized version of a problem that only applies to one company, or solve a problem excel solves better, or solve a problem which was just a bad (now permanent) process. The list goes on.

However it happens, you greatly increase your chances of providing a valuable piece of software if you have exposure to not just a single business in an industry, but dozens of them.