The investigator who knows the answer may notice different clues from the investigator who must discover it.

Knowing the answer changes what you see. Once the conclusion is fixed, details that support it become salient and the rest fades, and this happens without any intention to deceive, which is why someone approaching the same evidence blind will often notice a different set of things entirely. Expectation quietly edits attention.

When a question really matters, get a look from someone who does not know what you concluded, and do not tell them first. In your own reviews, try writing down what you would expect to find if you were wrong, before you go looking. The point is to give the disconfirming details a chance to be noticed.