These are things that happen when your friends and neighbours are open-minded, broadly athletic and generally fun.
You agree, over Christmas dinner and drinks and cake and games of Taboo and charades, because of a chance 'how about we', to run a half-marathon in 2013.
This leads to a discussion of training regimes and running clubs.
Which reminds you that there are two 30-40 mile bike rides you want to do next year.
So here's what 2013 looks like, from a 'this seemed like such a good idea at the time' perspective:
2 runs/week with Woodside-Sunnyside Running Club
Half-marathon by December
TD Five Boro Bike Tour - May 5
Ride to Montauk - May 18
Yoga (asana practice) every day in January
Start Ashtanga practice - Feb 1
Start Iyengar practice - Mar 1
Updates as they happen.