You never know how profoundly you can change someone's life, but it may take only a minute with a passing stranger on the street or a month with a friend struggling through depression, or it could take 40 years of consistent care, love, and attention with someone who you are dedicated to, no matter what comes your way.
Life is too short already, so I want to seize every moment (whether that moment lasts a short minute or that moment passes by as a 40 year memory, flying by faster than we know) and every opportunity to positively impact a friend, a family member, or a stranger's life.
Why not spread as much good as possible in this short lifetime? We may find that our actions lead to a chain reaction of more people on this Earth being inspired to change the lives of those that they interact with, or pass by every day on the street.
That sounds like a pretty good mark to leave on this Earth if you ask me!