Elon Musk is the world’s richest man—yet is typically pretty hush-hush about how he gives his money away. The Tesla CEO is worth a tremendous $450 billion, but in the past few years has only publicly donated a few billion dollars here and there. That pales in comparison to other billionaire donors like MacKenzie Scott, who’s donated nearly $20 billion just in the past five years.

Musk says it’s because philanthropy is difficult.

“I agree with love of humanity, and I think we should try to do things that help our fellow human beings,” he told Nikhil Kamath for the WTF podcast in an episode published Sunday. “But it’s very hard.”

Musk, who is on the path to become a trillionaire thanks to the approval of an historic pay package, says it’s “very difficult to give away money well.”

“The biggest challenge I find with my foundation is trying to give money away in a way that is truly beneficial to people,” he added. “It’s very easy to give money away to get the appearance of goodness. It is very difficult to give money away for the reality of goodness. Very difficult.”