If you do not like chess rules than try another game.
most annoying rule in chess
Interesting inquiry, though here's one way to think about it: If you did nothing about the discovered check the next move, then black would be able to take your king. Hence your king is in immediate danger of being captured. In other words, your opponent would be able to capture your king first, even though it'd hang his king the following move.
I (white) just received a check from a bishop, a discovered check from black's knight moving to E3. I got the discovered check but the bishop was pinned, and I don't think this should be a legal move, how can the bishop move to attack king if he is pinned, then knight takes my rook... totally a bs rule in chess in my opinion...