The researchers summarized: "A human mind is a wandering mind, and a wandering mind is an unhappy mind. The ability to think about what is not happening is a cognitive achievement that comes at an emotional cost.". Long ago, Buddhists reached much the same conclusion.
David Michie, Mindfulness Is Better Than Chocolate: A Practical Guide to Enhanced Focus and Lasting Happiness in a World of Distractions
buddhism, unhappiness