I once ran 10km by accident
I decided to follow my dad on a run in an attempt at father-daughter bonding. Erroneously thinking that his being 32 years older than me would give me an advantage, I set off on a light jog with Dad into the lovely Nottinghamshire countryside.
After a fair bit of running, I jogged alongside him and asked "Dad, how far are we running today? I normally run about 2 miles, maybe 3 on a good day."
We jogged on in silence for a few seconds, then he replied "Oh, this route's over 5 miles."
Faint heart never won bacon sandwich so I ploughed on, eventually running over 7 miles (although so slowly that I was overtaken by passing bumblebees). Moral of the story is always clarify with your keen triathlete father how far he's planning before you set off.
B x