Arousal theory is based on the ideas that different individuals perform better at different levels of arousal and that every individual seeks to find its optimum level.  Some people enjoy a quite evening to relax while others might prefer a loud concert to end a tough week.  This also explains the behaviors of thrill-seekers.  There optimum arousal level is high, so to feel comfortable they get involved in sensational acts.
     Another part of the arousal theory is the Yerkes-Dodson law.  This states that simple tasks require a high level of arousal to get the motivation to do them, while difficult tasks require low arousal to get the proper motivation.  You may have found that doing your boring busy-work homework requires a lot of effort on your part while doing a difficult brain teaser is fun and is easy to concentrate on.