When Thomas was first told about the meeting with Jesus that he had missed, he was understandably guarded. The notion that a dead man was back alive again was not exactly something you grabbed hold of and easily believed in a minute or two, not today and not 2,000 years ago, either. Modern scholars sometimes pet the disciples as such naïve bumpkins that they’d believe anything. Not so. They knew the dead stayed dead and this was not a fact you revised on a whim. So Thomas plays it safe but also then speculates aloud as to what it might take for him to believe this after all. As he talks, his rhetoric gets more and more exaggerated. "My friends, I'd have to see with my own eyes the nail holes in his hands. No, tell you what, I'd need to touch those holes with my own finger. Better yet, I'd want to stick my whole hand right into his side where the sword pierced him!" Thomas kept mounting up an ever-larger heap of evidence that he thought he'd need to believe. His words seemed calculated to induce some eye-rolling.
Of course, once he does meet Jesus, all that evaporates. To paraphrase a traditional aphorism, if you don't have faith, then there will never be evidence enough to convince you, and if you do have faith, no evidence is needed.
Without faith, no evidence is sufficient; with faith, no evidence is necessary.