One way to learn is to be very observant and open your mind to the possibilities of what the reasons might be. Not all of the possibilities will be the correct one, so you need to sort through those which don't seem to apply and isolate a few reasons that have the greatest likelihood of being the reason. Sometimes it takes a few rounds of trial and effort before you can pinpoint it to an exact reason. Being open to the idea that there is a reason is the first step.