Given the choice, would you pick Blue or Red?
Some people made their choice based on the cover stars of the game, Red contained the big dragon Pokemon Charizard, an obvious display of power. For those who picked Red based on this fact, it would have been an easy choice to pick the first in the line of powerful fire lizards.
For a while, it would have seemed like a perfect choice, Charmander learned to roast things pretty early and by the time you made it to Viridian Forest you would be spending an extended visit burning some bugs to the ground. It felt good man.
So you leave the forest and turn up to your first gym battle brimming with confidence, that's when it all starts.
"Fire types are weak to my rock-hard defence."
"But Charmander is strong as anything, he's a dragon-in-training!"
"Oh hai, this is my Onix."
So perhaps you beat Brock and feel validated that your Charmander is still the right choice. So you go to Mount Moon to beat on some more locals and are then faced with more rock-types looking to ruin your day. Okay, it's a tough moment but you're still going to get that awesome dragon in the end right?
Then comes Misty and her water Pokemon...
Then it hit you, maybe you should've picked the grass/water Pokemon instead?
Alternatively, look at how Charizard treat Ash in the anime, troll or trollest?