In science there are some researchers whom formulate or change their hypothesis after they have seen the results of their statistical analyses, also called HARKing. I want to point out a few options why some researchers show this behaviour. Maybe they are willing to change or formulate their hypotheses post hoc because they need to publish and therefor they need a positive significant result, because of publication bias. Another option is that they are ignorant to the fact that HARKing can be harmful to science and see no harm in doing it. But why is HARKing bad for science?
Because with HARKing a hypothesis is made after the results are known the chance of falsely rejecting a null-hypothesis increases, this means an increase of type I errors. Furthermore there will be a distorted image of effect sizes because effect sizes found will be larger than the true effect sizes. Another reason why HARKing is bad for science is that it increases the chance of wasting resources like time and money. This is because there are more studies that have to be replicated that have no true effect.
Luckily there are some good remedies against HARKing. For example, replication of research makes it possible to find if there was any HARKing. If ignorance of the consequences is the reason that some researchers HARK then education would be a good solution as well. But pre-registering of research is probably the best remedy for HARKing because this really minimizes the possibility to HARK.
Kerr, N. L. (1998). HARKing: hypothesizing after the results are known. Personality and Social Psychology Review, 2, 196-217.