You don't start at the top. Barriers really are incredibly low but that's not to say its realistic to expect to land enterprise clients on day 1. The key is o build a sustainable business and work your way up while creating that track record. I think we've gotten way too used to these overnight success stories about startups (which aren't really true a lot of the time).

I hate to use this example because its a bit cliche but Google entered late into a field of established players and won. Microsoft beat IBM (this one applies only to the PC, I know IBM is still a force to be reckoned with). Stripe, Balanced, and Square are able to compete with PayPal for accepting payments. I know these arent all enterprise-specific but I didn't take the parent's comment to be about enterprise only.