Patrick and John Collison founded Stripe in 2010. Fundraising was hard — the prevailing view was that PayPal had already solved online payments. The reality was that the existing system was a mess for developers. Accepting payments on the web required weeks of integration work, bank relationships, and painful APIs. Nobody had built it for engineers.
Within two weeks of starting, they processed their first transaction. The Stripe API launched with just 7 lines of code.
The big lesson: payments weren't solved, they were just tolerated. The problem was hiding in plain sight because it had always been painful and nobody expected it to be otherwise.