Because ageism is real. I finally got hired to a good job, with a boss who appreciates what I do, but before that happened, I got (rather snidely) accused of "googling the answer," had people blow off my phone appointment, was basically called a "fake programmer," and had people angry at me or look at me like I'm a piece of crap during interviews.

I have never, ever, been treated like this in my professional life, except in the Bay Area. Knowing what you don't know is generally best learned by getting some bruises in the process. Really, the lesson is that not knowing what you don't know can be very extremely painful. It's one thing to know that abstractly, another to know it from direct experience. There are some people who just knee-jerk say you can't do this or that. There are other folks who have enough experience to have a good feeling for how to navigate what they don't know, in such a way that the team can see it coming.