"Grave error" implies something that a non-fool might blunder into. Fools don't blunder, per se, they simply exist.

One of the first jokes I ever heard at a startup was "We'll give the product away and make it up on volume!" Changing the joke to "We'll pay people to take the product and make it up on volume!" doesn't make it less obviously ridiculous.

I'm amazed they were able to hire employees, let alone find investors. Doesn't make the guy's death any less tragic though.