"We tend to judge the probability of an event by the ease with which we can call it to mind."
What do you think is more likely; getting killed by a shark or getting killed by a flying champagne cork?
Most people swear that shark attacks are far more common. After all, there are movies made about shark attacks and there's ever a shark sighting near a beach, the media swarm and and sell us the bad news. In fact, champagne corks kill far more people each year than sharks.
That seems weird, right? Why does it make intuitive sense that sharks are very dangerous and that champagne corks aren't even worth talking about? It all comes down to how we recall information from our memories.
Recent Events Are Easier to Remember
Things that happened recently are fresh in our minds. We know they happened because, well, they just happened. Things that happened in the distant past are far more difficult to remember.
Moorhead, Minnesota (right next to Fargo, North Dakota) where I'm from occasionally suffers from severe floods. If you talk to people the year after a major flood, they tend to think that severe floods are very common and are likely to happen next year. If there hasn't been a major flood for a decade, people judge a major flood as being less likely. The closer the flood is to recent memory, the more likely we judge its likelihood.
Similarly, after getting a speeding ticket, many people will slow down and start driving a little slower. Over time, though, as the memory of that speeding ticket becomes more and more distant, people are right back to where they started.
Familiar Stuff Is Easier to Remember
If you were asked to judge how likely it is for someone to get divorced in their 60s, your answer (not the answer) will depend on how many people you know who got divorced in their 60s. If you know several couples who were divorced in their 60s, you will thinks it's common. If you don't know anyone in their 60s who got divorced, you will think it's unlikely.
When you're asked this question, you scan your memories for incidents of this happening. If you can remember some you think it must be likely.
Thinks that you know and are familiar with can be further broken down into preferences; things you like and things you don't like. You judge things you like as being more common and things you dislike as being uncommon.
What percentage of people like jazz? How about classical music? If you don't like jazz or classical music you probably think not that many people like it. You don't like it and you aren't weird. Plus, you don't know anyone who does like it, except for that weird uncle nobody talks about.
On the flip side, if you do like jazz or classical music, you probably think a higher percentage of people also like it. You are more likely to hang around people with similar music tastes and that gives you the impression that there are a lot of people who listen to those genres.
We Remember Things That Happened Directly to Us
If something happened to you or someone you love (good or bad), then you think it's far more likely than it probably is. Things that have happened directly to us feel like they are more likely to happen again, or feel like they were likely to happen in the first place, than things that we just read about.