That’s all. It’s not hard.
While driving is often mundane, even boring, anything unusual can happen at any time. An errant motorist can cut across your path. A child can dart into the road. A bicyclist, or motorcyclist, could swerve to avoid something you can’t see.
It is the responsibility of every driver to be present — in anticipation of the unusual — ALL the time. It only takes one person to avoid a crash.