Further we will see that it is very arguable point.
All cases of healing in Mark can be split into two broad categories: healing itself, and casting out demons and unclean spirits. The former one includes healing from fever, leprosy, paralysis, withered hand, haemorrhage, death, deafness, blindness, and in the latter one there are numerous instances of exorcism.
When Jesus cast out an unclean spirit in Capernaum, it "convulsing him [a man] and crying with a loud voice, came out of him" (Mk 2:26). Whenever we read about demons and evil spirits we must remember that it's a common reference for mentally sick people of ancient and medieval times.
Possessed ones actually had hysteria or various kinds of mental disorders (Crombie, 1964); belief in somebody's divinity could be a shock strong enough to cure themselves. It is important to note that at least in some cases (or even maybe in every one) it was a sick person healing himself, and Jesus was simply an agent, a catalyst.
Crowds gathered around Jesus, for they believed that even a touch of his clothes could remove disease (Mark 5:28). A woman suffering from haemorrhage was healed, or maybe we should say "self-healed" in this way - in Mark 5:24-34 it is clearly shown. The woman thought that she would be healed if had touched Jesus' clothes, she believed in it. Notice that the meaning of "belief" has at least two different meanings: you can believe that Earth is round (in fact, it's a flattened sphere) but it doesn't affect your feelings, since you're not an ancient astronomer questioning the contrary. And there is belief that is somehow connected with your welfare, health or even life. Sometimes it grows up to the stage of temporary insanity, and a stress situation can have a great impact on individual. In our case we see the latter situation: "your faith has made you well" (Mark 5:34). Then the author adds: "go in peace, and be healed of your disease" to emphasise the role of Jesus.
If we agree to the aforesaid, we must agree that disbelief works in adverse way. When Jesus returned to his hometown, there was no sensation, for they remember him to be just a son of carpenter. Men in synagogue demonstrated hostility against him and "he could do no deed of power there" (Mark 6:5), though healed a few people.
About the same way Jesus healed Simon's mother-in-law, who had fever (Mark 1:29); a paralysed man (Mark 2); a man with a withered hand (Mark 3:5); a deaf man near Decapolis (Mark 7:31-35); a blind man in Bethsaida (Mark 8:22-26) and near Jericho (Mark 10:46-52) and a multitude of people whose diseases are not mentioned. Actually, it doesn't matter what disease was healed; it matters, how it was healed. Sanders in his book "The Historical Figure of Jesus" (Sanders, 1996, especially chapter 17) goes further and also asks about perception specifics of ancient men, what they thought they saw and what really happened.
Why the blind man in Bethsaida wasn't healed from the first attempt There may be many suggestions, but I think it's because of author's attitude towards prayers. Compare the case of epileptic boy, when Jesus' disciples were unable to heal him; there Jesus emphasised the importance of prayer and faith. We don't have to pay attention on imaginary