I have always found that having something to look forward to and think about during the toughest moments of the day get you in the right mindset for tackling the day's challenges. This topic is discussed in several books, including Tools of Titans and Happy Money.
In Titans, Tim Ferriss references an interview where the guest constantly reminds himself, "Tonight I will be in my bed...tonight I will be in my bed" when going through a difficult situation during the day. Knowing that eventually you will make it through your toughest moments to something that you enjoy can provide the positive mindset needed to get through stressful situations. Personally, I like to tell myself, "At the end of the workday I will get to have my N.O. Xplode fruit punch pre-workout drink" which may sound random...but honestly tastes amazing at the end of a long day!
In Happy Money, Elizabeth Dunn and Michael Norton discuss the a concept of deriving pleasure from "anticipating the future." For example, most people who book a trip experience a happiness boost in the time heading up to the vacation. Often times, this feeling of excited anticipation can result in more positive feelings than the trip itself! Whether it is something as small as a favorite drink at the end of the day or something bigger like a weekend getaway, I have found that visualizing a positive experience during a moment of stress provides me with a booster-shot of positive energy needed to complete my work at a high level.