[jonhendry]

"Regarding "if you seem to have done everything correctly", I don't think that any honest scientist can claim that his/her study had no limitation or flaw."

Right, that's what I was getting at. The scientist might believe they've done everything right, after checking and re-checking their work, but be missing some flaw or limitation in their work, their model, whatever.

I recall hearing once of an experiment that couldn't be reproduced, and it turned out to be due to some chemical property of the entirely normal laboratory glassware that one lab had used. Switching to another manufacturer removed the problem. (I'm probably messing up the details, like the consequences of the chemical properties of the glass. But the gist is correct. Different manufacturer of glassware cleared up a problem that was unexpected.)