Bono admonishes his interlocutor with, 'don't say that later will be better', but later in the song goes on to contradict himself by stating that, 'it's just a moment, and a moment will pass'. If U2 doesn't hold the secret of happiness, who does?
Voltaire, that's who. But more on that later. First, our eponymous hero asks (Martin I think):

"Do you believe," said Candide, "that men have always massacred each other as they do today, that they have always been liars, cheats, traitors, ingrates, brigands, idiots, thieves, scoundrels, gluttons, drunkards, misers, envious, ambitions, bloody-minded, calumniators, debauchees, fanatics, hypocrites, and fools?"

I'd answer that yes, people have always done those things, but I'd argue that basically humans do whatever they can to improve their lot. In a well designed system, the cost of being a thief for example is too high and so instead it's in a thief's interest to abandon her life of crime and keep to the straight and narrow. What is a well designed system? Well, democracy helps, and an open and transparent and independent judicial system. Also, I think the aim of government should be to maximize individual freedom.

Philosophers tend to be better at asking questions than providing answers, so Voltaire surprised me at the end of the book. After the adventures of Candide and his companions had ended, they ended up at a bit of a loose end. They got bored, and rather directionless. Then a happy neighbour, a farmer, gave Candide the idea of having a garden for he and his friends to work on. Happiness ensued!