What is the dumbest mistake you made in Pokémon? (two of them)

My first Pokemon game is Firered, and I used the first six Pokémon I met. My team was Charmeleon, Ratatta, Pidgey, Spearow, Pikachu and Beedrill. I couldn’t get past Misty.

In my first playthrough of Emerald (after I gave up on Firered because I couldn’t beat Misty), I used a level 36 Swampert, a level 22 Beautifly, a level 18 Numel and a level 5 Nincada. Swampert’s moves were Tackle, Water Gun, Rock Smash and Mud Slap. The reason I chose them was because Mudkip and Marshtomb’s other moves did no damage or didn’t have 100% accuracy.