Pokemon has always been a series that has largely allowed you to explore each region however you like, especially nowadays as the games transition to an open world format. However, there have been instances where a Pokemon game doesn't want you to venture forth until you've obtained a particular item or talked to a plot important character, setting up a creative roadblock to stop you from progressing.
Most of these tend to come in the form of a Pokemon blocking your way (like Snorlax or Sudowoodo) or you needing a certain HM, but there have been many cases in which these roadblocks don't make that much sense. Pokemon fans have been sharing their favorite "dumb roadblocks" on the series' subreddit, showcasing just how silly they can get.
A popular choice for many on the subreddit is the irritated old man from Pokemon FireRed and LeafGreen. Annoyed that he hasn't been able to get his morning fix of caffeine, the old man lays down in the middle of the road while his poor family try to move him. Thankfully, he gets up and teaches you how to catch Pokemon once he's finished his coffee, although I'm sure we can all relate to that man's plight.
Another popular, and also very meta, choice comes from u/hjyboy1218, who brings up the absurd group of dancing men in Pokemon Black and White 2. These men will dance in a line to prevent you from going any further in your journey, knowing full well they're a roadblock for the player as they sing "We dance for no reason. We'll disappear for no reason" while blocking your path. Very funny, Game Freak.
Other popular choices include the Luminose City worker from Pokemon X and Y who stops you from exploring the city due to a blackout - despite there being a block of brightly lit buildings behind him - and the pack of sleeping Wooloo in Pokemon Sword and Shield that you have to walk around so you don't wake them up. There hasn't been a roadblock more effective than that in my eyes. Let those precious Wooloo rest.