Meetup : Complex problems, limited information, and rationality; How should we make decisions in real life?

Most decisions we make involve complex, poorly understood systems. We'd like to be rational anyways, but how?

Example time: I am going to pre-commit here to biking to the meetup. Why? I believe that more exercise would increase my physical fitness in ways that are beneficial.

But... I haven't done the research into the benefits of physical fitness, and haven't done a tradeoff analysis of time costs versus benefits, I don't know how likely dangerous biking accidents are in LA, I don't know enough about my body to be sure that biking is safe, or a useful way for me to get in shape. Should I spend the week until the meetup researching these factors and building a model, or should I spend time getting work and homework done, playing with my kid, and sleeping? Through a combination of trusting experts, laziness, and other things to do, I'm not going to do the research.

And that's where we are with most decisions. What should we do, if we want to be rational? I have some ideas, some questions, and some willingness to shut up and listen to others, and I might even update my beliefs if others have ideas I like.