I expect that people who regret missed opportunities more than actual behavior have higher estimates of the expected value of hypothetical actions than people who don't. That is, they believe the X they didn't do would have been totally awesome, whereas the Xes they actually did do have various flaws and blemishes.

I tend towards inaction, so I tend to regret inaction more than action - there's often been situations where I think I probably could have made a difference if I'd just gotten involved. That said, actions occasionally explode in BIG ways and form very lasting, intense regrets. I seem to handle the latter MUCH better than the former, though, so I'd still rather push towards action over inaction.

But, ideally, I'd like to push for "action, with 5 minutes of sane contemplation beforehand", because I almost never regret that - I often still have "learning experiences", but it's much easier to say to myself "Well, I did the best I could with the information I had at the time, and now I'll have a better model in the future".