We discard friendships and love because it doesn't "fit" us at that time in our life. We discard strangers, people who will never mean anything in our lives and we'll never be of any significance in theirs.
We also discard possessions that may or may not have had a meaning in our life, from a shoe worn by a homeless person and keeping them alive through the cold seasons to a plastic bottle, mindlessly discarded on the pavement by a passer by, too impatient to find a place to properly dispose of it.
We live in a world where everything has become disposable. Sentimental meaning and attachment easily disappears and everything can be discarded.