Can you remember needing something so much that you had to persistently ask your parents, which almost became a pain in the neck? As little children, we knew that persistence was vital to get our parents to do our bidding or to get approval for something. But there are some exceptions; though we bug them, they will not agree to grant our requests. This happens because our parents know what is best for us.
Our God is a loving Father who desires to give us whatever we ask of Him, especially if done in faith. We are confident in His power that we will receive whatsoever we ask of Him; thus, we approach Him with boldness. However, just like our earthly parents, there are instances when we do not get what we ask for.
God's response to our request is based on His perfect will for us because He knows what is best for us. Our requests are approved when they are in line with His plans for us. We get a No when they negate God's will, and He can make us wait if the timing is not right or a threat is imminent.
The gift of a car is good but not the best for a ten-year-old since it is not safe for him to drive; though he persists, no good parent would approve of that request. Likewise, God, in his omniscience, would give us the best gifts at the right time so that His name would be glorified.
God is always interested in giving His children the best gifts of life if only we ask in faith.

Dear Heavenly Father, thank You for the privilege of communicating my needs to You through prayer. I am grateful that when I call, You will answer and grant me my heart desires according to Your plans for me. Instill the mind of Christ in me so that my desires and thoughts are aligned with His. I place my confidence in You. Please help me to trust in Your best for me. Give me the grace to wait patiently for answers to my prayers. 
In Jesus’s name I pray. Amen.