לע"נ שמריהו בן חנה
Listen to the voice of my outcry my king and my G-d, for to you alone do I pray. [Tehillim 5/3]
Why should Hashem listen to my tfilla? Because all of my tefillos are in order that I recognize that you are my King and my G-d. It is not about getting out of you what I want but about establishing who is the true King. [See Mei Marom]
Also - The Maharal writes that a king is obligated to take care of his subjects. So to the extent that we accept upon ourselves Hashem's Kingship, he will take care of us and answer our tfillos.
Malki - my king who loves me. Elokai - My G-d of strength [Elokim denotes strict judgement]. [Mei Shiloach on Tehillim]
"For to you alone do I pray" - If we put our COMPLETE faith in Hashem, He will hear our prayers. But if we have other sources we believe in then Hashem says [כביכול] - "They can take care of you - see ya later".