That's a good point. It's good to be conscious of the fact that the person you're interacting with may not be in a healthy state of mind. Had the professor know

That's a good point. It's good to be conscious of the fact that the person you're interacting with may not be in a healthy state of mind. Had the professor known that his behaviour would cause such distress to Tim Feriss, he wouldn't have acted like that (so he is not guilty: he didn't do it intentionally). If we are all a bit extra nice on the off chance that the other person is depressed, that would not only help depressed people, but also people who are not depressed. But I can see how it can be hard to avoid feelings of guilt like that. Perhaps it helps to view it the same way as charity: you can donate to a charity for the third world poor, but that does not mean that you have to feel guilty about poverty that you didn't fix. Similarly, you can donate to the "happiness charity" without feeling guilty if you cannot prevent all suicides.