Solution density

In the real world, there are so many variables to consider that we'd never get anything done if considered all the options. Do we need to check the headlights of the neighbors cars to know if we should make oatmeal or pancakes for breakfast? Does the arrangement of dust particles on the back porch matter?

We're good at focusing on the important details. Along with our experience, that allows to make quick decisions.

I'm wondering what formulations exist for intractable problems in computer science that relate to solution density in the sparse area of world configurations that actually matters. Seems perhaps more meaningful than trying to measure actual problem size.