Reason 4: The scientist misinterpreted the results
Sometimes the scientific findings are correct but the way they are interpreted is not. I can give an example from my own scientific career as an immunologist. I used to study the response of a certain type of human blood cell (an NK cell) to malaria parasites. In one study, using microscopy, we were able to show that some NK cells attached to some malaria parasites. In the paper we wrote to report this, we speculated that perhaps the NK cells were in fact directly communicating with, and becoming activated by, the malaria parasite via a structure known as an immunological synapse. The reason we speculated that this might be the case was that if that was true it would have been extremely exciting (at least to nerdy immunologists like us!). However, subsequent experiments suggested that while our observation was correct (that some NK cells sometimes stick to some malaria parasites) our interpretation of the observation (that an immune synapse was being formed) was probably not. Our observations were correct, our interpretation of them was just wishful thinking!
Next — Reason 5: Someone else misinterpreted the results