A recent study out of U.C. Berkeley found that after a poor night’s sleep, people were more likely to think only about themselves and be less grateful toward their partners than when they were well-rested. A preemptive solution? Try making “thank you” an essential phrase in the morning. On the days you’re exhausted, it won’t come naturally, so try turning it into a game—each of you has to say thank you about something before you leave the house.