- They are searching for relevance.
- They have mastered the concept and are seeking a deeper meaning.
- They find the concept difficult and are trying to understand.
For reasons #1 and #2, asking "why" is an appropriate question. Provide context, make connections, explore examples and possibilities, etc.
For #3, if the student is struggling to master a new and difficult concept, asking "why" may actually lead to frustration, lack of follow through, and a less than expected outcome.
A strategy for those asking "why" about a concept that they find difficult to master is to redirect the focus to asking "what". Asking, "What do I need to learn?" (or a similar line of questioning) breaks down concepts into step by step pieces that allows for careful, focused efforts to result in gradual improvement.
I often use a cooking metaphor. At first, you follow the recipe to make sure you do it right and the meal tastes as it was intended. After a while, you know the recipe, how the ingredients taste together, etc. and can begin to experiment with new ingredients to improve on the recipe while minimizing the risk of total disaster.
Questions are important and can lead to deeper discovery. However, guiding students towards the most appropriate question can also improve success and motivate them to seek deeper meaning.