The problem goes beyond Chavez. Venezuelans have known about the issues of depending on only one export for decades. Thing is, no one was able or willing to do anything about it. Obviously the socialist doctrines that took hold of the venezuelan government weren't going to solve it, and as expected, made things much much worse.

Edit:

I think that there are two big problems with having your country depend on a single easy to obtain resource.

First, it doesn't provide incentives for society to improve its values, since the export doesn't require too much people with good values, and the consequences of failing to improve won't be felt immediately.

Second, it gives a big incentive to groups of corrupt individuals to seize power. If you control the money making machine, then you're set, you can make away with people since they're largely not part of the equation.

Venezuela's economic crises and food shortages started well before the oil prices declined. Chavez's failed economy theories created this problem.

The high price of oil was merely masking the disaster he created. It allowed massive cash injections and lavish spending on social programs to compensate for serious issues that price controls, import/export controls, corrupt nationalized businesses, mass emigration of top business talent, etc caused.

It would have failed eventually, it just would have taken longer. Venezuela is incredibly corrupt and more money would not have fixed that.

One could argue that sanctions only serve to increase corruption by eliminating non regime sources of income for the local populace.

Same could be said about Saudi Arabia, but that one has been working, in a fashion, for quite a while.