If you want to build a business, focus on what lies at the core of it. That’s the one thing you need to pick. “One thing” is at least 10.000 things that you have to do and get right in order to make that “one thing”. Doing two things, means twice that + complexity squared + negative attention span = disaster.
Just for fun, try taking the Venture Capitalist approach to picking the one thing:
Pick one thing, one product, one area, one niche, in which you can become #1 in the World. If you can’t become #1, you haven’t defined your one thing narrowly enough.
Less than #1 in the World is probably OK for most of us, but there is value in thinking it through to the end.
If at some point you fail doing that one thing, then try another one thing. Do many one things if you may, but do them in sequence.