A fellow toastmaster presented a thought provoking presentation about asking why five times which I found interesting.
For example, consider finding a spill in a store.
 You ask why is that there?
It may be there because someone spilt some soft drink on the floor.
 You then ask, why did someone spill soft drink on the floor?
It may be because a customer bumped into the customer than was holding the soft drink.
 You then ask, why did these customers bump into each other?
It may be because one of the customers was walking fast past some shelvings and didn't see the other customer going past.
 You then ask, why are the shelvings there?
The shelvings may be there as per request by head office.
 You then ask, why did head office request the shelvings be there?
It may be that head office is trying to sell more products.
You can go further and keep asking why, for example as to why they're trying to sell more products (perhaps to increase sales on particular products or on marketing's advice). You can actually do this at any of the points (1 to 5 in this example) of asking why and in doing so you can indirectly and directly change the chain of outcomes.
This questioning why technique can be applied anywhere in life, whether in business, or in your own life. It reminds me the sort of questioning we have as kids, why? 'Why is it like that?' I hope you find the technique useful. You may even consider as I have, the potential to expand this to other forms of the Ws (i.e. Who, when, what, where, why and how), but for now, I'll start with 'why'...