I have always said that most people are not going to understand that their actions have consequences until you hit them in the pocketbook. In the 21st century of the world, profit is everything. Kicking someone square in the wallet never fails to get their attention. And it never fails to get them to shape up.
Economic sanctions are not a completely effective tool, but one of many. There are other diplomatic tools required to motivate a leader to act a certain way. Even with all the options explored, sometimes that is not enough. However, sanctions have proven to be effective both on their own and partnered with other options.
No, economic sanctions do not prove effective in altering decisions, because it hasn't worked for how many years in Cuba? Opening up to the West and to money, like we did with Russia, is what works to make countries more open to the free market. Cutting off only makes them hate us.
I do not believe economic sanctions prove effective in altering decisions. I think we can see that with Russia currently. They've already come out and said that such sanctions would not be accepted. The same can be said with North Korea, while they may deal with them, they certainly don't act any differently.