"We think about the future in a way that no other animal can, does, or ever has, and the simple, ubiquitous, ordinary act is a defining feature of our humanity." - Daniel Gilbert, Stumbling on Happiness.
The ability to think is the gift. The fact that thinking can also bring a lot of grief is the curse. Why our thinking creates grief is the question. How to manage or change our thought processes is the happiness journey. [Russell]