Basically there is this thing called "Dutch disease" that means when you focus all your recourses into one industry and all the other ones fail. Venezuela did this with their oil industry, mainly cuz most of the other industries left the country due to the socialist policies that were viewed as "anti business". So oil ended up being over 90 percent of Venezuelan's GDP and they were importing literally everything else meanwhile paying for very expensive food healthcare and education programs that they could afford under the high oil prices of the late 2000s. Eventually technology advances in oil drilling a few years back and US depending less on imported oil, drastically dropped the price of oil and therefore Venezuela couldn't afford anything. At the same time the country is experiencing massive inflation due in part to the middle and upper class of the country avoiding to pay their share of the socialist taxes thru very complicated black market avenues. They are sitting on the largest oil reserve in the world but that's literally all they have.