He really is/was smart about some things - marketing and self-promotion. He started with millions and ended up with hundreds of billions, all thanks to his marketing skills, and knowing how to be in the right place at the right time.
Being good at one thing doesn’t automatically mean he’s good at other things - like running a company, or being an engineer as he likes to imagine himself.
Leave home to buy some spices, then go to a wrong grocery store and make a mess there breaking everything on the shelves