Indeed. My brother is training for his first sprint triathlon and he's putting in a hell of a lot of work (he hasn't managed to practice open water swimming yet because of the area he lives in but it's on the cards and he does pool sessions). He's signed up for this thing called "try a tri" where you do a novice triathlon, then he'll go for a sprint one. I asked him if he ever fancied doing an ironman and he looked at me like I was mental, and he's relatively fit (he's in law enforcement/defence, works out several times a week and used to be a competitive gymnast). It makes me laugh that someone who can't do 5k at a brisk walking pace thinks she's capable of an ironman.