ok the question is, do i have to? if i flip a coin and get heads with good rod do i have to pick a pokemon and put it on top of my deck. can i just ignore this and not pick a pokemon at all? and same if i get tails.
No, you HAVE to do what you CAN do. Therefore, if there is a Pokemon/Trainer in your discard and the coin gives you the corresponding result, you HAVE to take said card back.