The Shah's biggest mistake was hoping the countries oil wealth would sustain them, and he used the petrodollars to take out massive loans. My Dad was in Iran in the 70's and said the decadent wealth was beyond garish
He was not only spending much (on a borrowed money indeed), but he was also spending like an idiot. It's quite telling that his country struggled with accepting shipments because there were no suitable port facilities to unload and no suitable roads to transport.
Also, he bought a s**tload of weapons which were then laying in magazines, because his army was not trained for this. His solution? Train his people? No, just hire foreign contractors to operate it. It's almost as funny as Gaddafi purchasing a lot of anti-aircraft missile launchers just to have them stand by the coast, unmanned.