In order to be truly happy, a man must have everything done according to his will. If he faces opposition, his serenity is disrupted.
How then to be truly happy? Simple. We must conform our will to God’s will. Everything that happens is done according to God’s will, and if we would only unite with that will, we would then have everything done according to our wishes. If our only desire was for things to be done precisely as God wanted them done, we would get exactly what we wanted.
And that is how to be happy. Conform our will to God’s, and perfect happiness is ours.