...because it's a common way of trouble-shooting.
you start out with a decision tree in reverse; I have problem x, and the causes could be a-q.
It could be the computer
it could be the card
It could be software
It could be your phone.
You start lopping off 'decisions' (if i try it in another computer, and I get the same problem, then it's probably not the computer), until you get narrowed down to the offending bit.
If the problem doesn't follow you to a given component, that component can be eliminated as a potential cause.
If you have access to school, a library, etc., you should be able to get access to another computer. Those of use in tech support usually have access to more than one, and you're right, it's cheating...