I'm just coming to watch this thread for a bit to hopefully give me motivation to get going. Hopefully if you can all do it, I can too!
I would really like to be able to run 5k but I just can't and it's embarrassing. I can swim for hours and hours, and play a team sport (but just a fun one session a week type, no really serious training) and do dance classes. People at work try to persuade me to do charity runs and things and I just can't. I've done a relay triathlon a couple of times which was great because fewer people wanted to swim, but I feel like a "sporty" imposter when they start talking about running!
I think part of it is stamina. I have asthma, and had a couple of bad attacks, and now when I have to do anything that raises my breathing rate for an extended time I panic and stop! In a pool it's different because you have to time your breathing anyway so it's more controlled I think.
To add to my difficulties, I have a long commute, live somewhere with no pavements and the nearest park has had a lot of attacks recently, so as it's getting darker I really don't fancy going there... I'm thinking about doing it on a treadmill at the pool, maybe with a weekly run during the day at the park at the weekend.