Matteng this quote from the Hedonic Treadmill article is good:
Quoteone potential way to keep happiness from fading is to mix up the elements of one’s positive experiences so that they are less repetitive. Another approach is to try to appreciate such experiences even more by making an effort to pay attention to and savor what is enjoyable about them.
I personally feel like the concept of a "hedonic treadmill" is not helpful. Instead just think about how you want to move toward happiness (and enjoyment) and away from pain, and that it is a learning process that occurs through trial and error. Then, over time as you get older you become wiser and your happiness levels increase.
And this is: VS17. "It is not the young man who should be thought [most] happy, but the old man who has lived a good life. For the young man at the height of his powers is unstable, and is carried this way and that by fortune, like a headlong stream. But the old man has come to anchor in old age, as though in port, and the good things for which before he hardly hoped he has brought into safe harbor in his grateful recollections."
And from Letter to Menoeceus: "...Wherefore both when young and old a man must study philosophy, that as he grows old he may be young in blessings through the grateful recollection of what has been, and that in youth he may be old as well, since he will know no fear of what is to come. We must then meditate on the things that make our happiness, seeing that when that is with us we have all, but when it is absent we do all to win it."
The young man will learn much sooner what brings a life of happiness (through the study of philosophy).