Feels like you should take the advice even further for a startup. A startup shouldn't be going vertical or horizontal - a startup should be picking one individual problem to solve and focusing on only that.
Horizontal is close to impossible for a startup. The budgets involved don't usually allow for focusing on more than one product market at a time.
Vertical is also very hard. The startup would need to be in at least two different businesses to go vertical. Lots of IT/web startups do try this by being in both the infrastructure business and the software product business, with half of their startup aimed at creating new methods of managing servers and data, and half on providing some user software on top of that. There are lots of success stories here, but you have to assume there are lots of failures also who went overboard on building up a vertical where they didn't need the whole vertical to solve their actual startup goal.
Basically, I'd say in the same way a mature corporation is one that pays out in dividends any money that they can't get good return on, a mature startup would be one that focuses only on a single core business goal of some kind, and fails quickly if that business goal doesn't work. Vericals/horizontals can come after the startup phase and the business goal is met.
Horizontal is close to impossible for a startup. The budgets involved don't usually allow for focusing on more than one product market at a time.
Vertical is also very hard. The startup would need to be in at least two different businesses to go vertical. Lots of IT/web startups do try this by being in both the infrastructure business and the software product business, with half of their startup aimed at creating new methods of managing servers and data, and half on providing some user software on top of that. There are lots of success stories here, but you have to assume there are lots of failures also who went overboard on building up a vertical where they didn't need the whole vertical to solve their actual startup goal.
Basically, I'd say in the same way a mature corporation is one that pays out in dividends any money that they can't get good return on, a mature startup would be one that focuses only on a single core business goal of some kind, and fails quickly if that business goal doesn't work. Vericals/horizontals can come after the startup phase and the business goal is met.