On the one hand, I agree, we should all do everything we can to prevent suicide. It's the right thing to do, and it may very often be the case, as in the above account, that small positive actions can have disproportionate results.
On the other hand, we need to be diligent to avoid assuming responsibility for the actions of others. If we look at suicide prevention as an assumed responsibility, it can be hard to avoid feeling guilt when someone close to us takes their own life.
We should always be good to each other, and we should reach out to others in kindness, whether they appear to be in need or not. But, we should be careful with how we relate to the actions of others, lest we fall into a trap that we cannot get out of.
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.
On the other hand, we need to be diligent to avoid assuming responsibility for the actions of others. If we look at suicide prevention as an assumed responsibility, it can be hard to avoid feeling guilt when someone close to us takes their own life.
We should always be good to each other, and we should reach out to others in kindness, whether they appear to be in need or not. But, we should be careful with how we relate to the actions of others, lest we fall into a trap that we cannot get out of.