memory

Meditating really makes it clear how everything the senses encounter can get filed away indefinitely, along with whatever feelings they stirred. Try to sit in silence and you'll be assaulted on all sides with old memory files - nostalgic ones, anxious ones, happy ones, horny ones, scary ones, sad ones. On and on it goes in an endless stream while you're just trying to sit and breathe for a couple minutes.

Maybe that's one of the reasons the wise suggested guarding the senses. Being mindful of the input so the present moment can actually permeate awareness without being crowded out with so many obsolete junk files.