If you have to force yourself to act, then self control suffers (self exhaustion or „Ego-Depletion“), if after that is another challenge. It could be shown, that an emotional effort at the beginning of the experiment reduces the ability in the second phase to endure the physical effort involved in strength training. It is enough if we are challenged before the effort to have to choose between „virtuous foods“ (E.g. radish and celery) and chocolate or sweet biscuits. Who resists the temptation and remains „virtuous“ is faster with the following cognitive or physical task! But in addition to such serious decisions before the race there are still more strenuous situations that restrict our creativity, our conflict resolution skills, our logical thinking and may damage our athletic performance:

• when you try not to think about pink elephants
• when you try to crowd out emotional stirring thoughts
• unsolved conflicts you carry around
• if you want to impress others
• if you try to stay keen, when I’m feeling badly treated by someone

That overwhelms our nervous system. The value of blood sugar drops, if our self-control is demanded. In corresponding experiments could be demonstrated, that e.g. with glucose-sweetened lemonade can restore the ability to self regulate despite (pre-)load.

Source: Daniel Kahneman. Fast and slow thinking. Munich 2011