I not great with estimating sizes, and i often have trouble converting things from feet to meters on the spot. Last session i presented the players a quest to slay a sea monster. They cleverly decided to scout first with a familiar, and i described the creature and its size. I ended up exaggerating the size i bit too much and they’ve decided to avoid it until they’re higher level. So what was supposed to be a simple “monster of the week” type of encounter has now turned into a late game boss fight.