The Other Driver Broke the Law
When you are looking around and generally being alert while driving,you get to expect that the other drivers, cyclists and pedestrians are also going to follow the law. However, if the other driver's intended violation of the law is obvious, you don't get to expect they will follow that law. What went on in your specific accident, what the facts are, is really important in figuring this out.
For example, if you are driving on a street with no stop signs, and there are other streets that cross the street but those streets have stop signs, you get to expect those drivers on the cross streets are going to follow the law, and stop at their stop signs. But, let's say you are driving on the road without stop signs, and you see a car rushing up to a stop sign so fast you know they aren't going to be able to stop. In that case, you have to be the one to slow down, and take evasive action, because it's clear that they are not going to follow the law and stop. So you get to think other folks will follow the law, except for when it's clear to you that they can't or won't.