The 10,000 hour rule
This one gets repeated everywhere. When researchers went back and checked the original evidence, it did not hold up. The popular version is not what the data actually shows.
The idea is everywhere: put in ten thousand hours of practice at anything and you will become an expert. It came from a popular retelling of real research, and the retelling flattened it into something the original never said. The actual studies, of elite violinists and other performers, were narrower and more careful. They were about deliberate practice, a specific and demanding kind of effort: structured, focused on your weaknesses, guided by feedback, and often uncomfortable, quite different from simply accumulating time. And the researchers never claimed a magic number, or that practice was everything. Later work made the gap clear. A large analysis found that deliberate practice explained only a portion of the difference in performance between people, about a quarter in games, a fifth in music, and almost none in professional work, far from a hundred percent. The rest came from other factors. Ten thousand hours of ordinary, unfocused repetition does not make an expert, and the famous round number was never really in the science.
Simply spending a lot of time doing something does not make you good at it, and the popular ten thousand hour rule badly distorted the real finding. What builds genuine skill is deliberate practice, focused, uncomfortable effort aimed squarely at your weaknesses with real feedback, not the comfortable accumulation of hours doing what you can already do. This is why fifteen years of experience can amount to one year repeated fifteen times, familiar, unchallenging, and not actually improving. It is worth asking, of your own practice and of anyone whose experience you are weighing, whether the time was spent stretching into difficulty or just logging hours, because improvement comes from what you do with the hours rather than from the hours.
Source: Ericsson, Krampe and Tesch-Romer, 1993, popularised and distorted later. The correction: Macnamara, Hambrick and Oswald, Deliberate Practice and Performance, Psychological Science, 2014.
Ericsson and Pool, 2016
From the researcher whose work was misquoted, on what deliberate practice actually is and is not.
Draw your own card. It does not take long, and it rewards taking your time.