When you walk, usually you don't see the white shadow walking beside you who may stray behind a hedgerow or veer away into a dark wood or a tall city full of thrusting agendas different from your own, or into a love bower you left behind, or never made.
Your co-walker may swap places with another white shadow, and another. This is a parallel self who made other choices, who stayed with your former lover, or still works in the old job, or never crossed the sea, or chose pancakes instead of waffles for breakfast. Though the veil between you is thinner than shrink-wrap, you rarely see through it except in your dreams, where you enter the life of an alternate self who has trouble remembering the alternate self you inhabit this side of the dreamlands.
Yet when your paths converge with a parallel self, you feel something, obscurely, a tilt to the day, and may notice you are drawing events and encounters in a different way. People praise you or put you down in ways you can't fathom unless you awaken to how you are loaded now with karma of your white shadow incurred in adventures you can't know about until you follow the dream tracks of your multitudinous self.