Adreessen seems like he's working from a definition of "introspection" that is something like: "negative thoughts and feelings towards the self; unproductive self-criticism, regret"

In other words, a mental doom-loop. But that's not really what introspection means at all.

Healthy introspection is simply attention, curiosity and reasoning applied to the self. It doesn't have to be the kind of mental self-flagellation he suggests.

It is of course, incredibly valuable - I think its basically the opposable thumb of the mind.