It is probably not difficult to understand which car at an uncontrolled intersection has the right of way. When the cars arrive at different times the first in gets to go through. But when both cars arrive simultaneously it is the car to the right that has the right of way.
I think most people know that rule. So you might wonder why these accidents happen and it probably has much to do with driver attention and concentration. That might explain 90% of the uncontrolled intersection accidents.