He doesn't want to understand it. He wants to break through it and some sleazy and/or desperate engineers are telling him everything he wants to hear. They understand that it's impossible but they also understand that if they don't cater to his fragile ego they'll be looking for a new job and no job will ever pay more.

Elon legitimately believes that nothing is impossible because his entire life he's been able to pay other people to fix his problems for him and he can't handle the idea that he's not the most special important smartest boy.