This is a link post for "Salt, Sugar, Water, Zinc: How Scientists Learned to Treat the 20th Century’s Biggest Killer of Children" in the second issue of Asterisk Magazine, now out. The question it poses is: oral rehydration therapy, which has saved millions of lives a year since it was developed, is very simple. It uses widely available ingredients. Why did it take until the late 1960s to come up with it?
There's sort of a two part answer. The first part is that without a solid theoretical understanding of the problem you're trying to solve, it's (at least in this case) ludicrously difficult to solve it empirically: people kept trying variants on this, and they didn't work, because an important parameter was off and they had no idea which direction to correct in.
The second is that the incredible simplicity of the modern formula for oral rehydration therapy is the product of a lot of concerted design effort not just to find something that worked against cholera but to find something dead simple which did only require household ingredients and was hard to get wrong. The fact the final solution is so simple isn't because oral rehydration is a simple problem, but because researchers kept on going until they had a sufficiently simple solution.