Carrot then stick. Then carrot... Then stick...

Carrots work, but carrots don't taste so good after a while. Sticks work, but after a while the pain is numbed. 

If you want to change behavior, you have to learn to use both. Once the carrots start to get old, bring in the sticks. Once the numbness sets in, lay out the carrots. 

The US and Cuba opened their respective embassies today. We've gone far too long with only sticks, it's time for some carrots. But for carrots to be truly effective, you must have a big stick in your back pocket and be willing to use it.