A story worth pondering:

In the summer of 1942 [Edward] Adolph, a physiologist at the University of Rochester in New York state, wanted to find out how people could live and work efficiently in the desert and how to get the best out of them. …

Adolph was the first to test the presumptions most people still have about what to do if forced to make any sort of effort in extreme heat. Most, he discovered, were myths. Stripping to T-shirt and shorts, for instance, is not the best way to cope with dehydrating conditions. Long sleeves and long trousers may feel hotter, but they'll slow the loss of water. Nor is there any point in rationing water when supplies are low. Putting off drinking it merely makes you unhappier sooner. "It is better," wrote Adolph, "to have the water inside you than to carry it."

The most important of Adolph's findings was the simplest: drinking during exercise improves performance. Today, we take this for granted, but generations of coaches and distance runners were taught that drinking during exercise was for wimps. …

Adolph tested the old assumptions by splitting his soldiers into two groups. Both marched through the desert for up to 8 hours during the time of year when the average afternoon high was 42°C. The soldiers in one group were allowed to drink as much water as they wanted and the others weren't allowed any. The results were clear: the drinkers outperformed the non-drinkers. …

His findings stayed secret until 1947, when he was allowed to publish his pioneering Physiology of Man in the Desert. It went almost entirely unnoticed. In the late 1960s, marathon runners were still advised not to drink during races and until 1977, runners in international competitions were banned from taking water in the first 11 kilometres and after that were allowed water only every 5 kilometres.

So not only were authorities dead wrong, but they were so confidently wrong that, in the name of helping runners, they paternalistically forced runners to do the exact worst thing!  How could authorities be so wrong for so long on something that was so easy to personally test, and with such huge consequences?  And how could they remain wrong for three decades after careful study had proved them wrong?