You may think that telling students to strive for excellence is always a good strategy, but it turns out that it is not quite as simple as that. A series of four experiments looking at how students' attitudes toward achievement influenced their performance on various tasks has found that while those with high achievement motivation did better on a task when they also were exposed to subconscious "priming" that related to winning, mastery or excellence, those with low achievement motivation did worse. Similarly, when given a choice, those with high achievement motivation were more likely to resume an interrupted task which they were told tested their verbal reasoning ability. However, those with high achievement motivation did worse on a word-search puzzle when they were told the exercise was fun. The findings point to the fact that people have different goals (e.g., achievement vs enjoyment), and that effective motivation requires this to be taken account of.
Those less motivated to achieve will excel on tasks seen as fun
 The effects of chronic achievement motivation and achievement primes on the activation of achievement and fun goals.. Journal of Personality and Social Psychology. 97(6), 1129 - 1141.(2009).