Under some circumstances, a car may need to brake suddenly, like if a kid or deer or something runs out into the road, the car in front of you suddenly breaks down, a car suddenly swerves into your lane, etc.

And so you need to be allowing enough space between yourself and the car in front of you and paying attention so that you can stop in case that car does suddenly.

When they assign fault for an accident, it’s usually not 100% one party or the other’s fault. In a case where someone slams on the brakes for legitimately no reason, they’re probably going to be at least partially at fault

But regardless of whether they were or weren’t in the right to stop suddenly, if you were following too closely to stop in time or not paying attention, you’re also at fault because the accident could have been avoided if you had been doing your part.

You can’t control what the cars in front or behind you are doing, but you can control what you are doing, and if there was something you could have reasonably done to avoid the accident but didn’t, you’re going to be at least partially at fault.