If you can quickly think of examples of a thing, it will seem more common.
There’s an availability heuristic that will lead you to believe a rare event is more common if you can think of examples of its occurrence easily (such as airplane crashes).
The likelihood of people being a victim of a mass shooting is way smaller than the likelihood of their house being burglarized. But because we can think of mass shooting examples more easily, the two seem roughly equal in likelihood.
This applies more to System 1 thank system 2.