Years ago I heard a rabbi on the radio explaining why he believed we all have an obligation to try to be happy, even if we feel rotten. The rabbi's reasoning was this: If a parent is only as happy as his unhappiest child -- and, boy, is that true -- how saddened, then, must God be when he looks down on his querulous, stressed-out, complaining human family? It followed that as God's children we owe it to our father to cheer up and count our blessings -- not for our own sake, but for his.

You don't have to believe in God to see the sense of this, because it applies as much to the temporal realm as it does to the celestial. The way we feel affects the way other people feel. If we happen to live with those people, if we are, for instance, related, our happiness is likely to be as contagious as our gloom or irritability. Ergo, we should strive to be buoyant -- if not for our own sake, than for the sake of the ones we love.

Ah yes. The bountiful, life-affirming, pay-it-forward

circularity of this way of thinking is all very logical in print.

It is a good deal tougher to apply it to actual life, when, say, your shoes are pinching and you're running late and just as you're getting into the car where children are wrestling and giggling in the backseat -- instead of quietly and obediently buckling their seat belts -- your coffee sloshes all over your seat. Then you do not pay anything forward: You make the people around you pay, right then and there. Since you can't yell at the shoes or the clock or the coffee, you yell at the people in your car. No more are you the only member of your family having a lousy morning. Now everyone's miserable! Well done!

So it takes effort. Some friends of mine instituted a system when their children were small that was designed as much to help them control their tempers as it was to ensure their children's compliance. If a child resisted some command, the parents would say: "All right, buster, we can do this the easy way--" and they'd pause, ominously "--or we can do it ... the tickly way!" They opted out of the hard way altogether. Who would want to do anything the hard way? Even the threat of it brings on a sour mood.

It's rarer for people to exude gladness for the sake of strangers, though, which makes a particular cashier at one Bethesda Safeway so unusual. Everyone calls her Miss Crystal, and she's as sparkly as her name suggests. She greets everyone happily, every day. She remembers the old people, and the neighbors who've moved away, and the names of babies. And she sings out good wishes to their mothers -- "Hi, Felicity's mom!" -- when the babies are practically in high school. Miss Crystal may have her dark days, but you'd never know it from her unfailing good cheer. She's chosen the tickly way, you might say, and it fortifies everyone around her.

Meghan Cox Gurdon's column appears on Sunday and Thursday. She can be contacted at mgurdon@washingtonexaminer.com.