If you're thirsty, then you don't need the whole ocean, you just need a glass of water.
If you're chasing traction and growth, you don't need to go after the BIGGEST market, just the Minimum Viable Market for your Minimum Viable Problem so you can build, ship, and grow your Minimum Viable Product.
Then, it's a matter of S curves. As you begin to top out on one, you move into adjacency after adjacency.
If you have plenty of capital, maybe you can do 2 or 3 of these at the same time.