"It happened to someone I know"

For many people the habit has a starting point. A colleague went to the doctor with backache and was dead within the year. Your father ignored a cough. A friend of a friend was told it was nothing, twice, and it wasn't. After something like that, the official sentence about symptoms being rarely serious stops working on you. For that person it was serious, and you were close enough to see it.

I wouldn't try to argue anyone out of that experience, and I won't try here. It's worth being precise about what it teaches, though, because I think the habit takes the wrong lesson from it.

What went wrong in those stories was nearly always delay. Someone had a symptom and didn't take it to a doctor, or took it and didn't go back when it carried on. The lesson is to get persistent symptoms seen, promptly, and to return if they don't settle. I'd defend that lesson to anyone. It's also the lesson of the one look in chapter 15, where the whole point is to find the instruction and follow it.

None of those stories teaches that reading about diseases at midnight protects you. Your colleague's outcome wouldn't have been changed by an hour on a forum. If it could have been changed at all, that would have taken an appointment made sooner. So vigilance, in the useful sense, means noticing a change, giving it a sensible length of time, and then acting. Searching isn't part of that, and chapter 7 described how it can get in the way.

There's a second thing the experience does, which the memory research in chapter 4 helps to explain. One death that you witnessed weighs more in your mind than any number of people you never heard about whose backache was backache. That's how memory works, and it isn't a fault in you. But it means that your sense of the odds has been reset by a single case. Your colleague's story is one of the rare ones, and because you knew them, it has come to feel like what usually happens.

If a loss like this sits behind your searching, two things may help. One is to say so to your GP when you next go. "My father died of lung cancer and I get very frightened about coughs" is useful information, and a good doctor will take it into account in how they examine and explain. The other is to consider whether the fear is really about your calf at all. Grief and shock can come out as worry about your own body, sometimes years later. If that might be you, it deserves proper help, and chapter 18 says where to find it.