Never. Instead, I have come to believe He may not answer our prayers in the time frame, nor the manner we expect however. I think sometimes He leaves us 'unhealed' as it were, though able to cope, lest after being healed, we fall into a greater sin. Moreover, I think He may grant us a great freedom of spirit, though we retain that thorn in our flesh, which helps us to remain humble and dependent upon His mercy. In the Gospel, Christ healed persons who had been afflicted with ailments they suffered from for many years, which says to me we must never lose hope. I was encouraged after reading the following from the gentle Pope Benedict XVI:
THERE IS NO HUMAN CRY THAT GOD DOES NOT HEARArt: Madonna di S. Luca, Bologna, Italy. Prayers for the victims of the earthquake.
"Many times", the Pope said, "we ask God to deliver us from physical and spiritual evil ... however, we often have the impression that He doesn't hear us and we run the risk of becoming discouraged and of not persevering. In reality, there is no human cry that God does not hear. ... God the Father's answer to His son was not the immediate freedom from suffering, from the cross, or from death: through the cross and His death, God answered with the Resurrection".
Finally, "a believer's prayer, if open to the human dimension and to creation as a whole ...does not remain locked in on itself. It opens itself to share in the suffering of our time. It is thus converted into ... the channel of hope for all of creation and an expression of God's love that is poured into our hearts by means of the Spirit". - Vatican Information Service