When you smile, don’t hold back. Show as many teeth as you can. See if the observer can count at least half your teeth when you beam at them. A smile is infectious. But rather than a nasty virus, you’re spreading mirth and merriment.* And if you can smile even in the worst of circumstances, then you’ve truly mastered the secret to a happier life.
*Even if you have poor dental hygiene, people will still return your smile, though they may back up a step or two.