"I don't believe it. Prove it to me and I still won't believe it"

This quote by Douglas Adams recommends that the speaker is highly hesitant and requires a lot of proof prior to they will accept something as true. It implies that the speaker is not quickly convinced and needs a great deal of proof prior to they will believe something. This could be interpreted as a challenge to the person making the claim, as the speaker is essentially saying that they will not accept the claim until it is shown to them. It might likewise be viewed as a sign of caution, as the speaker is being careful not to accept something as true without very first confirming it. Eventually, this quote suggests that the speaker is not happy to take anything at stated value and requires a great deal of proof prior to they will accept something as real.