Buddha told us that desire is the cause of all suffering. Desiring any one thing or more will always lead to suffering. By desiring some things and not desiring other things we open ourselves to the idea that we can receive things that we don't desire making them bad in our mind and therefore something that should be avoided. The things we desire become good to us and we don't believe we are able to be happy without them.
When we desire anything, we can never be satisfied, we can never have enough. We desire money and when we get it, it is never enough, we always want more. Take one look at all the billionaires trying to become trillionaires, we can clearly see that even when having billions of dollars which is more than any human can spend in many lifetimes, still isn't enough. We want to be Loved, but no one can ever seem to do it right or just how we want it done. We desire to control external circumstances and yet we never can.
We desire sex, always wanting more, never having enough. We desire God and therefore we fear satan. We desire peace and become afraid of war. We desire to be remembered which causes us to be terrified of being forgotten. We desire joy and loathe any other emotion. On and on and on our desires go, never being satisfied, always chasing, and always running away. We are all free to desire anything we choose, and God will let us do so as long as we choose to.
In truth there is nothing to desire because we are all in heaven and we are all enlightened and we can't desire any one thing because we have everything. Thinking logically, we are all part of the same universe which is made up of everything within the universe. Being part of the universe in which we are in, we literally have everything within the universe, known and unknown. We not only have everything, but we are everything itself.
When we desire any one thing within the universe, we cause a split within ourselves. Our "true self" knows that it has everything and is one with everything, and the "ego" believes it is separate from the universe. The "ego" believes this since it thinks that there is any one thing that could be separated from the universe and given to the individual "ego" in order to make the individual "ego" special in some way. Since the "ego" believes that something else could be separated from the universe, the "ego" also believes that it can also be separated from the universe causing confusion and disease.
In order for the "ego" to survive it always needs to be desiring some thing. The "ego" doesn't even know what it desires, it just needs to desire. If the "ego" appears to achieve it's desire, it will only transfer the desire elsewhere. There is literally no one thing that can satisfy the desire of the "ego" since everything is part of the same universe, and yet the "ego" never stops desiring. As long as we chase our desires and run from that which we don't desire we keep the "ego" "alive" within our minds and will feel split. It is an impossibility to have some thing that someone else doesn't have and by believing that we can we suffer. We live in misery since we suffer. We suffer because we desire.
"Ego" death is simply letting go of all desires. Desires come from the "ego". Some psychedelics can help us to achieve (meaning letting go of desires) "ego" death, when that experience comes, all desires vanish, and reality can be seen and is seen as one thing instead of separate things. Everything is God, everything is one universe, desire is the belief that any one thing can be separate and if any one thing can be separate, all things are separate. We then think that we can be separate from the very universe we are in we have a constant inner dread since we don't think we will ever be able to get back into our own universe that we never left. Love and peace!