Elon Musk does not separate his business and personal lives. In an encounter detailed in writer Walter Isaacson’s upcoming biography Elon Musk, Gates discussed philanthropy with Musk and suggested he donate to efforts for refugees, American education, and climate-resistant seeds—but Musk wasn’t having it. “Sorry. I cannot take your philanthropy on climate seriously when you have a massive short position against Tesla, the company doing the most to solve climate change,” Musk wrote, clearly salty about Gates’ half-billion dollar short against his company. Gates told Isaacson he apologized to Musk and explained his decision was based on his anticipated price drop from the supply of electric vehicles surpassing demand. “Once he heard I’d shorted the stock, he was super mean to me, but he’s super mean to so many people, so you can’t take it too personally,” Gates said. Musk previously tweeted that he found out about the short “from multiple people at TED” and asked Gates because “it’s not exactly top secret.”