It depends on how you define "successful". Lot of definitions:
1. Building a six figure revenue for solo bootstrapped founder. Work from anywhere, no team and make enough to live comfortably and travel the world.
2. Build a small company with 1-10 million in revenue. Need a small team for that. Possibly some Angel funding.
3. Build a 10+ million revenue company. Need bigger teams and possibly VC funding for quick growth.
4. Build a 100+ million revenue company. 1000s of employees. Almost definitely need VC funding.
5. Build the idea behind a company, create a product that shows tremendous traction and then SELL to another company. Profit for founders even though no real value created over a long time.
Take your pick. Each option may have a different path. I would love to be in the 4th one and still working on how to get there :)