Having the ability to think about or focus on the things you want to focus on rather than having outside forces dictate what your forcus.
People who can compartmentalize have the ability to ignore the storm surrounding them. They don't worry about what may happen but instead just deal with the very moment they're in. "Living in the NOW".
Some people however consider this ability as "living in denial" or "avoiding their problems". However to operate under pressure one has to be able to block out all the "noise" or "distractions" to be effective. You have to be a little delusional to accomplish greatness.
The only alternative is to allow yourself to become paralyzed with stress, negativity, and worry over what may or may not happen.
Now is all that matters until the next moment arrives.
The difference between success and failure is how one handles stress. The rainbow always comes after the storm.
"Worry does not empty tomorrow of its sorrow. It empties today of its strength." - Corrie Ten Boom