For the unaware, his mom was an acquaintance of the IBM CEO by virtue of both serving on the board of United Way, and Microsoft came up in conversation between them. A few weeks later IBM contracted Microsoft to write the operating system for the first IBM "personal computer".
He also promised to deliver the operating system within an insane deadline. He did so by by purchasing 86-DOS [0] (also known as QDOS) for $50k ($148,931.42 today) and porting it over to IBM PCs.
He got business connections with IBM, he is a skilled negotiator, he got an expensive education paid by his parents, founded his own business with his parent's money (do you have a $150k allowance?) and knew intelligent but "poor" people who were even more skilled than him who he then could hire to actually do the important work.
