Of the philosophical options, we prefer the idea that the best life is a social one. Yet even that has its drawbacks and difficulties. Social life is no more ideal in this world than the solitary life. The household, for example, is no haven of peace and rest. Friends and family turn on each other and bring the worst sorts of strife imaginable.
Just as the household, so the city does not provide the good life we yearn for. It too is full of fighting and murder and crime and all the sorts of things we're trying to escape. Augustine uses the example of the Roman law that requires torture in order to provide testimony from witnesses--which means that innocents are often tortured. If nothing else, what shall we say about the judge in such a place? He is inherently being unjust if he follows the law, and of course breaking the law if he does not follow it. What can a Christian say when he finds himself in such a position (either of judge or of the one being tortured) other than "Deliver me from my necessities."
Rising from the city to the cosmopolitan world, even there we find that there is no ultimate happiness. "As with the perils of the ocean, the bigger the community, the fuller it is of misfortunes."
Whether these are the language barrier, war, injustice within the empire, massacres, and the evils that even just rulers have to perpetuate, we see that there is to be no peace and no happiness in the wide-open world:
Any man who will consider sorrowfully evils so great, such horrors and such savagery, will admit his human misery. And if there is any man who can endure such calamities, or even contemplate them without feeling grief, his condition is all the more wretched for that. For it is only the loss of all humane feeling that coul make him call such a life 'the happy life.'