Spot on.

I worked on three different startup ideas unsuccessfully before moving into an existing business. I learned a little in the unsuccessful startups but not a great deal - it's hard to learn when you don't have a great amount of traction / users etc.

When I moved into the existing business suddenly I learned how to sell, how to work with customers, how to position the brand etc.

I wish I'd sucked it up and taken a more junior role sooner - I think I would be further along by now.