Ferruccio Lamborghini was a self made millionaire, he made a fortune by building tractors from army surplus left by the Allied Forces back in 1945. He started this business from a small garage but soon was able to move to larger buildings because demand for his very powerfull tractors rose.
He also started manufactoring oil burners and airconditioning systems after his tractor plant started making lots of money, it turned out his second business also made big money so Ferruccio Lamborghini became one the wealthiest men in Italy. He could afford just about everything he wanted, including high speed GT cars like the Mercedes SL300 and Ferrari he owned alongside the Jaguar he liked very much.
But his Ferrari started giving problems with the clutch, the local workshop couldn't fix this problem so Ferruccio decided to drive to Modena and confront Enzo Ferrari himself.
But Enzo, who was known for his arrogance, told this 'farmer' to take a walk, Ferruccio was furious and at that moment decided to show Enzo how he should build GT cars.
Of course this is a legend, and the thruth about it could be a little different, it was obvious that Ferruccio had lots of money to spare and the GT car market was still open for new things, money could still be made by building high speed, well finished cars, so it is more likely this persuaded Lamborghini to start his own company.