In the manga "Monster" that I am reading, the doctor is taking fire arms training from a veteran who lives in a rural area alone with the orphaned child of someone he has killed during a war.
The Veteran (A healthy man in his 50s or 60s) tells the doctor that the girl never smiles and feels that she will always despise him as long as he lives, he himself being a hardened veteran does not break expression. During his stay, the doctor shares his native lands cooking (Japanese) with chopsticks provide and the little girl takes to it quite easily. The Veteran struggles, dropping food which prompts the doctor to snickers. One day the Veteran returns to find a note (A letter of parting from the doctor) and more Japanese food which he shares with the girl. He still has not mastered the use of chop sticks which causes the girl to snicker and smile. This causes the veterans eyes to tear up with joy.
The light hearted and kind doctor infected those around him with his positivity without realizing it. Positivity is infectious. It goes straight to the heart and spreads to those around us. It is not something forced but that naturally intertwines into our system, going from one person to the next.
My theory is that we should try to be positive, enjoy life and indulge in happiness. It will spread and effect our actions passively. Before we know it we will be surrounded by positivity, seen in those around us. So don't "Try to do something positive or nice." just aim to be positive.
Let's start a pandemic of joy.