Eternally happy is a man who has nothing to lose. He can write, he can dream, he can laugh and he can sing. There is no sadness upon which he has not touched or sadness doesn’t exist for him(which happens very rarely). All the emotions, feelings, desires, passions have been overcome by him.
Thus, he his happy. If he fails, then he also he is happy. If he passes then also, he is much happy.
It’s an unimaginable and unique situation. We all try to be eternally happy so that we can keep our boats rocking but very, very few are always and truly happy. They are so happy that when darkness creeps upon them, that also brings them enlightenment and they remain happy.
There is another gateway of being happy always and forever and that is having the privilege of being with God.