What are some important issues that OPEC must confront in their efforts to control oil price?

cheating among cartel members - they all restrict output to keep prices up, so if one of them increases output, he will gain a lot and cause others to loose profits.What are some important issues that OPEC must confront in their efforts to control oil price?
I think the big issue that they discovered in the 70's was that too high of oil prices will cause a reduction in the output of the developed countries, which means they can't afford as much oil. In other words, the demand for oil in the long run is more elastic. Also, people will develop alternatives to oil. And, also, as someone else mentioned, cheating is important.What are some important issues that OPEC must confront in their efforts to control oil price?
I think they must lower the oil prices by more production and do least foreign investments in property and finance of trading the stock markets and hedge funds and US treasury bonds. Based on the economic theory of demand and supply, we should stop buying new and big cars until it really needed. I think OPEC should refuse or control the oil money investment into their crude oil barrels. How can they overcome their human natures of greed and selfish, till their crude oil running out and turn into fear?