I'm writing this in the African bush, where I've just watched five lions dismantling a dead buffalo, a hungry leopard stalking impala, and several baboons snitching part of my own breakfast when my back was turned. Out here, my safety depends on the knowledge, courage, and selflessness of just a few human beings. Some of these people I know well; others I've barely met. We are of various colors and creeds, sharing only a conflict-riddled ancestral history. Yet I feel safer at this moment than I once felt in my suburban American bedroom. It's not that I'm blind to life's fragility or the dangers around me. It's just that I possess a gift offered by many mistake-filled years: At my age, I have a pretty good idea what and whom to trust.

It's because I've learned to depend on a handy little inner mechanism—you've got one too. Call it a "trust-o-meter," a bit of hardware preinstalled on your hard drive the day you arrived, tiny and vulnerable, from the stork factory. Ever since, your trust-o-meter has been programmed up the wazoo, first by caregivers, then by you yourself. If your inner software is working well, your trust-o-meter is guiding you safely through life's many hazards. If it isn't, you smash into one disappointment or betrayal after another. The good news is that no matter how faulty your trust-o-meter, it's never too late to debug the system. Trust me on that.

Or not.

Read this; then you make that call.

Next: Testing the System