LOL. The secret of their success is that they visited Xerox.
That is so blatantly wrong that I laugh out loud every time some one throws it in the mix. The boys from Apple paid Zerox for what they used, you might note that Zerox had not a clue what to do with what they had.
You should of course include in the mix how Bill Gates stole(Actually bought) the original DOS. He was clever enough to only license it to IBM and those Savvy old boys agreed to it.
Apple started the Lisa project in 1978 going in this user-friendly direction. After the paid visit of Apple engineers to Xerox for some more inspiration, Apple produced something that did much more on less expensive hardware (Lisa was $10,000, Xerox system was $17,000). Apple then managed to squeeze the GUI down into the $2,500 Macintosh at a time when the DOS-based IBM PC/AT, with a slower CPU but with other specs a bit better, cost $4,000.
A bit later, Microsoft tried to copy Apple and produced a far inferior product on equivalent hardware. That's the difference between mere attempts to copy and getting inspiration for further innovation.