Put yourself in Chael Sonnen's shoes for a second. You are a wrestler and you know that you do should never use a Thai plum against a wrestler because the wrestler will go for a double and put you on your back.
The plum is a great t technique but not so much when your back is against the cage. Muay Thai based fighters do it all the time. But wrestlers typically fight for underhooks and will not go for a plum unless their opponent has double underhooks.
So you Chael Sonnen fighting Jon Jones who besides being a great wrestler is also taller and everybody knows that the plum is more difficult to apply against taller opponents. Nevertheless you go for it and get taken down. The rest is history. You lose.
You now fight another wrestler in Rashad Evans and he pushes you against the cage. And what do you do? You just go for the same move, you use a Thai plum. And you get taken down. And if that is not enough, obviously, you still did not work on getting up when you are on the bottom against the cage.
So what does this prove? It proves that although Chael Sonnen is a great fighter he is not a smart one and does not learn from his mistakes. Hard work and talent are great weapons in a fighter's arsenal but using your mind is the greatest of them all.