Once after dealing with a blind man, Jesus asked him if he could see anything. The man answered that he could only see people like trees. Then Jesus had to lay hands on him again and this time the man could see everything clearly. What happens now if a 'healing preacher' insists that someone can see normally when he cannot, or if the blind man says he cannot see even after the preacher has laid hands on him? The preacher may say that the man has no faith or has some unconfessed sin. (That is another subject.) But what if he insists that the man has been actually healed or healed in the spiritual realm and that he has to confess that?
That is the confusion about faith. Are we expected to confess we are healed, when we can see we are not? Jesus did not say that to the blind man. Once when He healed ten lepers, He told them to go and show themselves to the priests who had to certify that they were healed, and as they obeyed Him and went, they got healed. Even here, He was not asking them to claim or pretend they were healed before they were healed.
Faith is not make-believe where we force ourselves to believe that something is real when it is not, hoping that by doing so it will become true. Wouldn't it be a straight lie? We can say we believe Jesus is able to heal us or do any other miracle for us, but that does not mean that we can say we have been healed when we have not. Faith is based on facts. In this case the facts we believe in include God's ability to heal us, His heart of love towards us, etc. In other words, this faith is our confidence in Him as a person. We trust Him as we know Him and then we place our confidence in Him.
Even when we are fully convinced about God's ability to heal or do any other miracle for us, one thing we may not know at different times is whether He will actually do it for us. Our faith in God as a person we have come to know is one thing (He.11:6). If we have to have faith that He will indeed heal us, or do a miracle for us, that has to be a special faith, or a gift of faith which gives us an assurance that He will do it (He.11:1). If God speaks to us and gives us that assurance, then we will know it will happen (Ro.10:17). Then we can confess that it will certainly happen. But even with this, we cannot say it has already happened.
"Therefore, I say to you, all things for which you pray and ask, believe that you have received them, and they will be granted to you" (Mk.11:24). This is not positive thinking, but it is a trust in God that finds rest after leaving the answer to the Father.
The three men facing death in the furnace had faith in God as a person. But at that moment they did not know what exactly He would do (Da.3:17,18). Just because they believed that God could do miracles, they did not confuse that with being foolishly sure that it would happen.
One character of God is righteousness. He will not ask us to do anything unrighteous such as denying reality.