People tend to think of miracles as conclusive proof of the supernatural. The problem is that they are only proof to people who accept them as proof. Whenever anyone claims to have performed a miracle, some people might believe in the miracle, but others will believe that the occurrence was an accident, or a fraud, while others will believe that the occurrence was simply the scientifically predictable result of the specific actions which led to the occurrence.
Consequentially, the “reality” of a miracle depends more on the state of mind of the observer than it does on the actual events which take place. If the skeptical observer has decided beforehand that the “miracle” cannot be real, there is nothing that the person performing the miracle can do to convince the skeptic. The skeptic will come up with a non-miraculous explanation, even if it is simply, “I do not presently know how that happened, but I am convinced there is a non-miraculous explanation.” In other words, the skeptic will take a leap of faith to avoid taking a leap of faith.
Perhaps Jesus was thinking along these lines when, as recorded in Mark chapter 8, he responded to the Pharisees who kept badgering him to perform a sign from heaven: “Why does this generation want to see a miracle? Let me tell you that this generation will not get to see a miracle.” It takes more than a few miracles to change behaviours and thought patterns which have been formed over many years.