I've seen a lot of guides (and some main sources like [LoLCounter](http://lolcounter.com)) where you can see what champion you need to use to lane against a particular champion. I've also heard a million players say that "I cannot do anything against this player — he's my counter".

Now, how do you know that a champion is another champion's counter? Like, for example, how do you get to the conclusion that - for example - Ezreal is bad against Miss Fortune?