Now there was a man in Jerusalem called Simeon who was righteous and devout. He was waiting for the consolation of Israel, and the Holy Spirit was upon him. It had been revealed to him by the Holy Spirit that he would not die before he had seen the Lord's Christ. Luke 2:25-26

What is it that you are waiting on God for? Imagine waiting and waiting until you are old for God's Promise to be revealed. Imagine like Isaiah, getting the promises but never seeing them come to fruitation. I admire Simeon. He has two things I fear I do not have; faith that God will keep His Promise, and a total focus on the Lord.
I have waited for a few years for my financial status to change. I have prayed. I have waited. I have had faith. I have totally lost faith. Part of this is due to my own foolishness, I must sadly admit. Part is due to circumstances beyond my control. Nevertheless, the bills keep coming in. I have been paying atrocious amounts to payday loan places to maintain loans that I cannot yet afford to pay off, yet cannot afford to keep- if that makes any sense at all. I have given up wondering just when it is that the Lord will intervene in this mess; I just know He is faithful, and keep praying. I fish into the past for reminders of how He has met my needs before.
It would be nice to be more like Simeon. His mind, his desires were not on earthly things, but on God. He did not want a new tent or a new camel, but instead his greatest desire was to see the consolation of Israel- the Promised Messiah. That's where his heart was. That is where his hope lay. In the end, in the temple, his Greatest Desire came into being as the infant Jesus was laid in his arms.
Again, what is that thing you are waiting for? Money to pay bills? A spouse? A spouse to accept the Lord? Family members to accept the Lord? A career opportunity? What is that "one" thing you are waiting for? Has God promised it to you? God has promised me that He will take care of my bills, yet I wait. And wait. Then I remember Isaiah being given promises that he never saw fulfilled. And Simeon given a promise that he had to wait his entire life for. Both of these promises had significantly more spiritual value than what I am waiting for.
If God promises you something, it WILL happen, just not in your timing and in the way you expect; but it WILL happen. Like it happened to Isaiah. And Simeon. And you.