Pessimism & possibilities

I've gone over this in my mind a million times.
There is this person that nourishes the opinion that one should, at all times, be on one's guard for any harms that might befall one. If things are good, or just bearable, she takes care to remind you that everything might change for the worse. Look out! I have a hard time trying to figure out what to say here. It is all too easy to presuppose that pessimism enjoys the support of Reason and Good Sense. Isn't it a good thing to watch out for possible difficulties, to be prepared for whatever situation that you may be confronted with?

Thinking about something is often thought to be a quite innocent business. "Thinking about bad things is no guarantee that bad things will happen." But preparing for future disasters is, as it were, an expression of one's perception of the present situation. It means quite a lot that we see something as a possibility in relation to which we see ourselves forced to take a stand. It's not innocent at all to view something as a possibility. What is more, to talk about something as a possibility has, in order to be taken seriously, to have some connection with the way we perceive the present situation. If it does not, I would say that you are simply playing with words. Of course, it is possible that I will be hit by a car tomorrow or that my colleague will put poison in my drink or that I will not be granted another scholarship ever again. But thinking about these things as real possibilities would have quite serious implications for the ways in which I think about my life, my colleague or my work.

My point is that it does not make any sense to say that one sees it as important to talk about possibilities while at the same time reassuring one that this talk is to be understood on a purely abstract level. If you say to me that you think you will probably have a brain tumor in a few years time, then I am, naturally, worried about you. I wonder why you think about this now. I wonder whether you are afraid of having a tumor. If you say that you entertain these thoughts because it is good to prepare for any scenario, but that it doesn't really mean anything specific, then I really do have a hard time understanding you.