Long before Elon Musk was running multiple companies at once, his mother, Maye Musk, had a much simpler recommendation: pick one.Elon Musk’s mother, Maye Musk, joined FOX Business’ Stuart Varney on "Varney & Co." to discuss her son’s ambitions, his childhood and the advice he ignored before taking on some of his biggest ventures.Maye recalled a conversation with Elon after PayPal, when he was weighing what to pursue next."And that…came later after PayPal, when he said to me, should I do electric cars, or rockets, or solar energy? And I say, you've just worked so hard, just do one. So you s...