The Shikkerdovid’s all time favorite pasuk is the taken from the Rebukes. (It should have been the name of a rock group in the early 60’s). The pasuk says: In the morning you shall say, give me the evening and the evening you shall say, give me the morning as the because of the fear in your heart. I believe the expression “being happy in the moment” is an outgrowth of this pasuk.
Rashi says this refers to growing fear and distress which will make you wish for earlier times. He quotes the Talmud in Sota. The mishna states “Rabbi Gamliel that says since the destruction of the Temple there is no day without a curse.” The Talmud interprets this to mean that every day will feel progressively worse.
The SD would like to weigh in. There are people in the world that despite all the gifts, pleasures, and benefits they have are never happy. Whatever they have, wherever they are, whatever they are doing.. they simply want something else. They cannot be happy “in them moment”. As this pasuk infers, in the morning these people think they will be happier in the evening.
The curse is that despite all you have, you cannot appreciate it or enjoy it. Wherever you are, or whatever time it is, you long for something else. As Rabban Gamliel says in the Mishna, since the destruction of the Temple, there is no day without a curse means that without a spiritual center or nexus, we can never be fully satisfied, understand or appreciate the gifts gd gave us.
The ultimate curse to humanity is never being happy or satisifed “in the moment.”