The 2-4-6 game
The 2-4-6 game has two players: one takes the role of Nature and the other takes the role of Researcher.
Nature writes down a rule for a triplet of numbers to match or not.
R asks N about a few triplets one at a time to see if they match or no, such as 1-3-5, 1-2-3 etc, and N answers "Yes, that fits the rule" or "No, that doesn't fit the rule". Then R guesses the rule.
(DON'T READ THE BELOW if you haven't played the 2-4-6 game before)
Trick is that Nature wrote the rule "any integers in increasing order", and R will tend to guess a much more convoluted rule. The game demonstrates how important it is to seek disconfirmations of R's hypothesis (Attempt to falsify), which would narrow down the search-space quickly, but people rarely do. This is "positive bias".
Positive bias (doing only confirming tests) can be regarded as distinct from confirmation bias (trying to preserve the belief you started out with), even though many times when there's positive bias, there's confirmation bias too. This game is an exception: no one would say that R is already trying to "preserve a belief" – R doesn't care about the belief for its own sake yet, so the problem is nothing so sinister, only that she uses a naive methodology.
Q: what should the existence of positive bias lead me to NOT see?