Poor sleep can impair gratitdue towards romantic partner

This article discusses research showing that poor sleep quality can impair your ability to show gratitude to your romantic partner. Seems self evident to me. I wonder, though, if a lack of gratitude is really just a part of the persons personality, and not just a function of sleep quality. Perhaps poor sleep quality just accentuates the problem. But selfish people are going to be selfish - good sleep or not.