INCONVENIENT BARRICADES
Pokemon, as well as many other franchises such as Fire Emblem, are notorious for this cliche. What is it exactly? Well you know how there's a really cool item right over there that you can use to become more powerful? Yeah, you can't get to it because of the little kid learnign to tie his shoe in the middle of the road. Yes, he takes up the entire road. Yes, he is five. Yes, when you obtain another element "crucial" to the plot, he will have tied his shoes and be standing by the side of the road so you can finally pass. What's the point of being the hero of an RPG if you can't even politely ask a little kid to let you passed so you can, oh, I don't know, save the universe from unending darkness? But na, that kid really just needs to tied his shoe. Or an old man i laying in the street until he gets his coffee. Or you can't advance towards that castle until you take a different one, thus allowing another event to take place and a new enemy force to spawn.
More examples here because I'm lazy and/or tired:
http://tvtropes.org/pmwiki/pmwiki.php/Main/InsurmountableWaistHeightFence