However much effort you think it will take to build a new business - multiply it by 10, and you're probably still underestimating it.
I don't just mean a new "startup". I mean a new business model (E.g., a B2C company trying to kick off a B2B product. A product company adding a new product to its suite, etc.)
So many founders and execs stumble blindly into these decisions without understanding the resource requirements and corresponding resource contention that will not only undermine the success of your new business but also crush the rest of your company as well.
Any time you have a meaningful difference in 1 or more facets of what you're doing (new market, new problem, new business model, and/or new product) - this is basically a new "business." It requires new efforts across everything from engineering, product, go-to-market, customer support, maintenance, and so much more.
Here's the real sneaky truth. Each of those facets doesn't have to be that meaningfully different. Each difference is multiplied by the others. It gets REALLY meaningful, REALLY quickly.
FOCUS.