What's the difference between fashion jeans and normal jeans?

Hey, I have a huge interest in clothes but I don't get why people spend hundreds of pounds on jeans, when any good shop will have a pair that fit and look decent.

I once when I was younger ignorantly bought some £210 jeans from a charity shop for £5, and they lasted a lot shorter than any other pair of jeans I bought, and tattered surprisingly quickly, (I also wonder about people who by plainest clothes for fashion labels)

what's the difference between fashion jeans and normal jeans?

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Maybe your jeans didn't last long cause you got them from a charity shop.

The price.
I buy my jeans from Marshalls for like 20$ a piece and they have lasted me almost a year.