When I was in my early twenties, I prayed for my niece and she died. My first funeral was for her. I didn’t understand it. My son, Chad was healed the first time I prayed for him and then he wasn't the second time. When he was four hears old, he had failed he pre-school hearing exam, and medical people said that he would need a hearing aid. This really bothered me. So I prayed over him and said basically "In the name of Jesus, Chad's hearing being healed." About an hour later, he came out of the bathroom and said "Daddy, when I flushed the toilet, it sounded real loud like an airplane taking off." With my lightening quick mind, I thought to myself, well now that's kind of strange. Then it dawned on me that God had healed him. Then about three years later, he had to have tubes put in this ears due to frequent ear infections. I prayed for him and he wasn't healed. Why was he healed the first time and not the second? Sound familiar. God showed me during this seven year period. The first time I prayed for Chad, it was done in a simple, child-like faith on my part. I just put it on the back burner and forgot about it. The second time, I thought about it, stressed about it, and it didn't work. The first time there was no unbelief present, the second time there was. Unbelief is the main culprit that blocks healing, and keeps our mustard seed(child-like faith) from working.
Matthew 17:20 says So Jesus said to them, “Because of your unbelief; for
assuredly, I say to you, if you have faith as a mustard seed, you will say to this mountain,
‘Move from here to there,’ and it will move; and nothing will be impossible for you."