"Consider a turkey that is fed every day. Every single feeding will firm up the bird's belief that it is the general rule of life to be fed every day by friendly members of the human race 'looking out for its best interests,' as a politician would say. On the afternoon of the Wednesday before Thanksgiving, something unexpected will happen to the turkey. It will incur a revision of belief."
- Nassim Nicholas Taleb, The Black Swan, p.40.
Just because for every single moment up until now there has been no evidence that humans don't have the turkey's best interests at heart, doesn't mean it is not possible.
No black carrots have ever been sold in your local grocery store store (or suburb or state) is not the same thing as black carrots do not exist.
No cancer cell has been detected is not the same thing as there is definitively no cancer.
Test scores show no improvement in learning from Classroom Practice X is not the same thing as Classroom Practice X produces no improvement in learning.
Confirmation bias is our tendency to keep searching for evidence that corroborates with our pre-existing belief rather than searching for evidence that might prove that belief wrong. Only looking for orange carrots won't prove that black ones don't exist. Yet, from Taleb again, those "discomfirming instances are far more powerful in establishing truth" (p.58).
Beware the motherhood statements of what works or doesn't work in education.