You're a primitive human in the wild. You're hunting, tracking the prey for a long time. You get distracted and start doing something else. You die. Perhaps even your entire family may starve. This is why it's a disorder across very different environments. It can affect the person's ability to cope across extremely different environments.

Likewise, if you have impulse control problems with your ADHD, you might not be able to prevent yourself from making a noise or movement at the wrong time, scaring off the prey or getting the attention of a predator (like a lion). Well, there goes your survival once again.