Is there really anything sadder than a lonely person? God did not make man to be alone (Gen 2:18). He made a helper for Adam and he created all of us to be helpers to each other. I like to think of v.10 literally. Think of a old man, walking with a cane, and he slips and drops the cane and he has no one there to help him up, imagine people walking by, not even giving him a second glance.
We all fall down, emotionally and spiritually, and it is absolutely vital that we have a person to turn to in those times.
Hold on to those people.

Ecclesiastes 4:7-12