Because, if you can't keep one friend's secrets in a different box from another's, you'll never have more than superficial friendships. People will learn that y

Because, if you can't keep one friend's secrets in a different box from another's, you'll never have more than superficial friendships. People will learn that you cannot be trusted and won't tell you anything important, particularly if you ever publish things. There are all kinds of things I know that I cannot publish, or repeat from one friend to another; that's the price of intimacy. Because the ability to change your focus, your attitude, or your mood – to adopt, perhaps, a wholly different personality – by changing contexts is a superpower, not a liability. Put me on the karaoke stage and I'm a big ham; put me in a suit and I'm a professional; put me in a library with a math book and I'm a mathematician; put me in the kitchen with a chef's knife and I can make dinner. I don't try to solve complex math problems on the karaoke stage, and if I can't stop thinking about cooking in the library I'm not going to enjoy doing math problems. My programmer self turns out to be annoyingly nonverbal when he's focusing, so it's a good thing he's not always around or my poor friends and relatives would never hear from me. And because the idea that one has a unitary, consistent, conscious personality is ultimately an illusion anyway. I've read enough psychology and philosophy to know this, but I've also met enough Alzheimer's patients to understand this. There are other reasons, but this is a start.