Playing on your point of luck - I recall reading in a biography of Gates that his mother was on a charity committee with the exec at IBM that was tasked with outsourcing development of an OS for the IBM PC. Anyway, they got the contract, provided DOS to IBM - and compatible vendors - and the rest is history. We don't know - of course - how much that pre-existing relationship influenced IBM's decision and we don't know if Microsoft would have had the explosive growth they did without that contract, but it definitely looks like the stars aligned.