I think part of the reason, a big part of the reason, is that when our minds wander, we often think about unpleasant things, and they are enormously less happy when they do that, our worries, our anxieties, our regrets, and yet even when people are thinking about something neutral, they're still considerably less happy than when they're not mind-wandering at all.
Creo que en parte la razón, en gran parte la razón, es que cuando nuestra mente vaga, a menudo pensamos en cosas desagradables, y somos enormemente menos felices, nuestras preocupaciones, nuestras inquietudes, nuestros pesares, y aun cuando las personas piensan en algo neutro, son bastante menos felices que cuando no se encuentran divagando en absoluto.