Must we assume that every time we prayed, it was in faith. Can we actually claim that our faith is perfect, never doubting?  What an arrogant notion.  Would we have walked on water longer than Peter did, or would we have doubted as he did and been rebuked by Jesus as having "little faith" (Mt 14:31). I think it's very possible that many of us would have sunk at some point, just as he did.  Acting on our faith is not always easy.  Doubt creeps in on a dime, especially when the waves start crashing against us.  Did not James warn us in the first chapter of his epistle:

5 If any of you lacks wisdom, let him ask God, who gives generously to all without reproach, and it will be given him. 6 But let him ask in faith, with no doubting, for the one who doubts is like a wave of the sea that is driven and tossed by the wind. 7 For that person must not suppose that he will receive anything from the Lord

We must admit, it is easy to doubt God will heal or grant wisdom at times, especially when you doubt that healing is even a promise to the new covenant believer. How could you ever pray in faith if you don't know healing is God's will? You can't. "Faith is of things hoped for a confidence, of matters not seen a conviction" (Heb 11:1, Young's Literal). Without being sure healing is God's will, your prayer for healing is a prayer of hope, not faith. Faith has a confidence in that which is hoped for; a conviction of the end result. Faith believes that what is prayed for comes to pass (Mark 11:22-24). Faith believes it receives. Hope just goes to the elders and hopes the prayer makes them better.  Those healed by the prayer of hope are being healed at the shear mercy of God, just as Peter was saved from drowning by the shear mercy of Christ, even though he doubted.  There will come a time, however, when those who are immature in faith will be expected to rise up and act on their faith.  Let's rise up and place our full trust in Christ!