Shoe life expectancy

I expect whatever it is I buy to work for me. I expect a good run out of my little or big investments, the way I measure them is through cost per wear (CPW). However I always stop to ask myself: how long is this suppose to last ? In this case, precisely: How long are shoes supposed to last ? Having worked for several years in the shoe industry it is a question I had not stopped to ask myself until now. Lately I have been noticing that my shoes have a tendency to fall apart, wether cheap or expensive. Wether leather, plastic or pleather, if you want to get fancy or textile, they just don't hold up. They should, most have some brand backing them up and it's not...