It is very easy to forget this simple statement. Research requires that something is known about the system. If studying mating behavior, at least one needs to know how to tell males from females. All of these need to be carefully investigated before the actual experiment is designed. Need a working hypothesis.
Hypothesis is a tentative proposition that subject to verification through investigation.
It must be possible that the test results do not support the hypothesis. But if we said males or females have a faster heart rate it could not be proven false and is not a valid hypothesis. You can, however, reject a hypothesis based on the data from an experiment. We could then do an experiment by pulling out 10 balls from the bag. If the all the balls that we pulled out were black, we cannot prove the hypothesis, but if one of the balls were red then we could reject it.