So often we are inclined to think that the only answer God can give our prayers is "yes." We need to remember that "no" is an answer also. "No" is certainly an answer of love on the part of our Heavenly Father when we ask Him for things which are not really for our good or for His glory. God does not always give us what we want; He gives us what we need. Just as a good parent does not grant all the requests of his child, God does not answer every request in the way we desire.
When we think of "unanswered" prayer, it may be that we do not understand the way in which God responds to our requests. He may not grant an immediate answer, and sometimes our prayers are answered in a way that we fail to recognize. We pray for prosperity, and sometimes financial stress is given. But our souls are made stronger for the test. We pray for health, and affliction is given, and we are better able to sympathize with those in affliction. God makes no mistakes, though at times we may question His wisdom.
Our motive for making a request to God must be pure. If your prayer is self-centered, concerned with the gratification of your own desires, God cannot, in faithfulness, grant your requests. James 4:3 says, "When you ask, you do not receive, because you ask with wrong motives, that you may spend what you get on your pleasures."
Perhaps you are praying for a person close to you, and you have not seen any changes. God can work through your prayers to soften a heart or to bring about circumstances to draw those for whom you are praying closer to Him. However, God has given man a free will. If your prayers are not always answered as you expect, it is not because God is not working in the situation. It may be that the person for whom you are praying has not yet responded to God's call. You must not permit yourself to give in to despair. You should, however, continue in prayer, knowing that the Lord is more concerned for them than you are and that it is His will to help them; read 1 Timothy 2:4, 2 Peter 3:9, and 1 John 5:14-15.