Crossing the street in traffic

Crossing the street in traffic....
We've all done this: you’re in a hurry, so instead of waiting for the “walk” sign you look both ways and see that the nearest cars are far enough away that you can cross safely before they arrive where you are. You start walking and (I’m guessing) make it across just fine.

1. Did you know (with absolute certainty) that the cars you saw in the distance weren't moving fast enough to hit you? If so, how did you come to know this? If not, how could you possibly justify making a decision like this, given the extremely high stakes? After all, you were literally betting your life ...
2. Can logic help us understand how a rational person could make a risky decision like this, despite not having perfect knowledge of all relevant factors?

The street-crossing example is chosen for the vivid consequences of making a wrong decision,
but less dramatic examples would make the point. We almost never know with absolute certainty what the consequences of our actions will be, but we usually manage to make reasonably confident decisions nonetheless — and most of the time we choose right. This needs explaining.

Original Source:
Probabilistic reasoning and statistical inference:
An introduction (for linguists and philosophers)