Kant's famous advice to the world on how best to live was to always treat human beings, including yourself, as an end and never a means to an end. That means never to exploit other people as a way to get money or fame or whatever, and, indeed, never to exploit yourself either. Of course, Jesus had also said: treat others as you would have others treat you. (Which is fine as long as your not a Sado-Masochist.)
Hegel and Marx pointed out that the human individual is what he or she does. The person\subject is not inside the human being, ready made and always the same no matter what that human being does. No, the person is always in the process of being created - by his or her actions. By their labour (and labour simply means any human activity, including thinking.)
So, is it not true that if you sell your labour as a means to an end (to get wages), that you are selling yourself, and treating yourself as a means to an end? After all, you spend most of your waking day getting ready to go to work, going to work, working, coming home from work, and then being too exhausted to do anything else after work.
If work is to be regarded as a means to an end, i.e. wages, then the people who do that work are also a means to an end.
And this holds for all types of human labour\activity. If we are not in the process of self actualisation in our everyday lives, then we are becoming alienated from ourselves, and becoming a pawn in someone else's game.
And that is the simple reason why capitalism must fail as people become more and more self aware, and demand that they be treated as an end in themselves and that they treat themselves as an end in themselves - not a means to the capitalists enrichment and their own daily survival.
Communism is the word for that form of society in which human beings treat themselves and others, in the words of Kant, as ends in themselves, and not means to an end.
And what is that end that the person must be? What is it to treat yourself as an end and not a means to an end? Hegel points out that:
"Mind is only what it does, and its act is to make itself the object of its own consciousness."
This sounds complicated but really it not. In the old days a carpenter made a table. He put his heart and soul into that work, like an artist, and he made a table that was an expression of himself. When he looked at that table he could see before him a physical manifestation of his own mind. As Hegel put it; the table had become, for that moment, the mind of the carpenter physically before him as he consciously regarded and appreciated it.
How different for the tens of millions who slave away for wages, making things that could never be regarded as an expression of themselves. What about the poor worker who makes police batons, decides to go on strike, and then has his head split by one of the very police batons he himself made. Thats what you call the alienation of labour.
Unfortunately, in the USSR and other states who aspired to Communism, the worker was very often also alienated from his labour. His labour was not an expression of himself, but, as in the capitalist system, was turned against him. The Workers State became the end to which the worker was a means to. Clearly this was not what Marx had in mind.
What todays Communists must do is create work practices and methods of production that put the productive forces in the hands and the minds of the workers themselves - so that our work becomes the physical manifestation of ourselves, and so that we work to see ourselves in our work. That is the great challenge which Capitalism must always shrink away in guilt from, and which Communism must happily make reality.