Do you know what you want?

Well, here I am after a gap of almost a month. I do not know if you have missed me. If you have then I thank you. Anyways, let us get to the point of discussion.
All through our life we have yearned for something or the other. If we are broke we yearn for money, if we are rich we yearn for fame and power. If we have given up all worldly desires we then yearn for the ultimate knowledge. Anyways, whatever stage of life we are in we yearn or desire for something we don't have. I think you would all agree to this. Even if a person says he desires nothing more his desire will be that he retains all the happiness he has and since the future is not in his hands he is still yearning for something he does not have.
But let us say we get what we want then most of the time life turns into an irony as we will either not be in a position to enjoy that we have always desire thus of no use to us or that desire is no more what we want. This has always happened to me and I am still experiencing it. Eventually most of us if not all don't know what we want because of the above two reasons.
Let us take a example, in our young age we have always desired to be treated as an adult and shoulder responsibilities but when we become adults we desire to be a child devoid of any responsibility and return to the age of innocence.
So all through our life we are always in search of something which eventually is of no use to us. So then we come to the same question I asked in one of my earliest posts. What is the purpose of our existence? Also, does this irony not indicate that fate or destiny has a lot to say in our life. I am sure that lot of you might have a different outlook altogether. But just give my view point a thought and let me know what you think.