Fume events are rare as long as you define them as being above regulated threshold of contaminants in the cabin. This is fine for most people, but others (my partner included) have sensitivities to the contaminants, which trigger neurological symptoms whenever she flies, even in "safe" conditions. These days she wears a mask whenever flying and doesn't get symptoms - except the 787, where it's not necessary.

Before we worked out the issue (the risk of which really should be communicated by airlines) she was sicks for weeks after flying. And although unlikely, she once was caught in a fume event and couldn't work for months. Others on the plane were badly affected too. This is serious stuff and the 787 is great progress.

It's true that fume events are rare, but they do happen. It seems that leaking seals are one cause. If you search aviation incident databases there seem to be one or two reported fume events somewhere in the world per month on average, which is indeed a tiny incidence compared to the volume of air traffic.

There is actually quite a few fume evenths monthly, and a rather concerning report[1] from one of them.

[1] http://avherald.com/h?article=4b6eb830/0006&opt=7168