- 30 years ago, you couldn't buy sports shoes (sneakers, runners, tennis shoes, court boots, whatever) that have only a foam midsole, no hard rubber outsole of any kind. A very light, foamy type of running shoe called a "race flat" did exist, but you had to go to a specialist store to find that. Without an outsole, EVA foam wears down fast. Stay away from these shoes unless you're looking to use them as bedroom slippers; always look for an outsole. If the shoe is not for a specific sport, look for trail runners, which have more outsole coverage on the bottom, often an uninterrupted one piece outsole.

- Most shoes today that look like they have a thick sole are actually hollow. If you peel off the layers of insoles, you see that the outsole is "ice cube tray" shell with voids. When the thin bottom of this tray wears through, they leak water. It just has to wear through in one spot, like the very back of the heel, and it's done as far as resisting water, and when it wears some more, rock can actually push up into the voids. All this can happen well under a year. I distinctly remember growing up with shoes that were solid, heel to toe.

Oh wow, it has it's own wikipedia page. https://en.wikipedia.org/wiki/Boots_theory