He knows if we are being honest or not. With God everything is open. Well, Our Lord Himself instructed us to ask that we may receive. He said this even though He affirmed that our Father knows what we need before we ask. But He wishes you to pray for this reason, that He might give you desire, and that His gifts might not be lightly esteemed.
Prayer is a two-way street.
We ask for things from God while, at the same time, our prayer is asking things of us. Prayer is a transforming experience. As St. Augustine said, God works on our desires. He stretches our desires or charity. Encourages us to grow.