How is it that the internet can do such wonderful things yet stores/online sites cannot deliver goods?

Question

catalogue orders that appear to be in stock online /you order then a few days before you require them they say out of stock- surely they should have een reserved for you when you order them.

Answer 1

please note that some companies do not carry stock themselves and rely on others to supply the goods for them.  

This is frequently the case for newspaper special offer where facilitators like Westex act for them. (Westex is actually quite good at delivering).

Also queuing theory is not perfect and unanticipated disruptions may affect sources of supply or delivery services

Also some businesses are over-optimistic and try to run before they can walk and end up not having the manpower or resources in place when they suddenly become popular.

Answer 2

Their operations managers don't understand queueing theory.

It's actually quite a bit of math and nuanced understanding of Poisson distributions and statistics to get these forecasts right.

Businesses try to keep their inventory as low as possible because it costs them money to hold it (called "inventory carrying costs").  The problem is that if they keep too little inventory, the run into stock-outs.

Operations managers who know what they are doing can use mathematics to ensure whatever service level the company needs.  If they don't understand the math, they'll get it wrong.