It feels good to buy things because it fills our ego.
We are made of egoistic desires to enjoy through acquiring, buying and receiving, and when we bring desirable things closer to ourselves in such ways, our egos enjoy for short periods of time.
The fulfillment is short lived because our ego is interchangeable. It behaves like a taxi meter. The wheel keeps turning, and our satisfaction diminishes with every passing second.
And what happens after the enjoyment fades away? We then need to work again in order to buy again. Our entire lives then look like an endless cycle of working and buying, working and buying, ad nausaem, and we never remain satisfied.
We cannot stop this process because our ego constantly grows. We always move away from a prior state where we had felt some fulfillment, enter into a feeling of emptiness and lack, and this lack forces us to seek fulfillment once again.
Moreover, since our ego constantly grows, then the pace of this process constantly accelerates. The time shortens between one purchase, i.e., a moment of pleasure, and the next such moment. Every successive pleasurable moment is half of the previous moment.
For instance, if we needed to travel on vacation for a week once a year, we now need to travel for a month in the summer, and then a month in the winter, and we continually need to find new and different ways to satisfy ourselves due to our constantly growing ego never letting us be completely satisfied.
Why do our lives operate in such a way? Why does our ego constantly grow, making us feel empty after every fulfillment?
It is because our ego grows in order to make us want the greatest fulfillment and force that we could possibly ever feel.
If we do not reach the final complete form of fulfillment, we leave our ego empty, and its vision remains fixed on the complete and continuous form of fulfillment beyond the smaller pleasures that enter it time and again. Therefore, it is as Kabbalist Yehuda Ashlag (Baal HaSulam) writes:
Since all their possessions are for themselves alone, and ‘he who has a single portion wants a double portion,’ one finally dies with only ‘half one’s desire in one’s hand.’ In the end they suffer from both sides; from the increase of pain due to the multiplicity of movement, and from the regret at not having the possessions they need to fill their empty half. – Kabbalist Yehuda Ashlag, The Study of the Ten Sefirot, Part 1, “Inner Reflection.”
Therefore, our life story is that we chase pleasures more and more, buying more and more, and the enjoyment we receive from this chase becomes lesser and lesser. Moreover, the intervals between each pleasure become shorter.
We can see an example of this loop in the rise of drug legitimization: that the usual pleasures people could once fulfill themselves with no longer satisfy them, and the ego demands ever more pleasure in shorter intervals.
We thus see that we are in a process of constantly-diminishing pleasures and a constantly-increasing feeling of emptiness, and it is in order for us to eventually reach a final state of despair—a state where we will want to bury our ego and shift to an entirely new and different form of fulfillment: not of receiving—but giving—pleasure.
This transformation from enjoying through receiving to enjoying through giving can be thought of similarly to how we become parents. As parents, we shift to a mode of enjoying from giving to our children.
It is a purely psychological inversion, a new mode of sensing pleasure. Instead of receiving pleasure into ourselves and experiencing that pleasure disappear, leaving us empty, we rather feel pleasure in a new attitude, where the more we give to the world, the more pleasure we feel. Moreover, we can feel the latter form of pleasure continuously, without it fading away.