5 Whys
The 5 Whys is a method used in both Six Sigma and Lean Production as a way to get to the root of the problem. The first thing you need to do is to state the problem. For example, let's say that a machine just broke down:
#1: Why did the machine break down?
It stopped because it didn't have any oil.
#2: Why didn't the machine have any oil?
The person responsible didn't oil it.
#3: Why didn't the person responsible oil the machine?
It wasn't possible for anyone to access the oil filler.
#4: Why couldn't the oil filler be accessed?
The machine sellers / manufacturers hide it.
Although in this case there are only 4 whys, the fact is that you already have 2 solutions for the problem: you can either call the machine seller / manufacturer or you can try to open up the machine and look for the oil filler.
#1: Why did the machine break down?
It stopped because it didn't have any oil.
#2: Why didn't the machine have any oil?
The person responsible didn't oil it.
#3: Why didn't the person responsible oil the machine?
It wasn't possible for anyone to access the oil filler.
#4: Why couldn't the oil filler be accessed?
The machine sellers / manufacturers hide it.
Although in this case there are only 4 whys, the fact is that you already have 2 solutions for the problem: you can either call the machine seller / manufacturer or you can try to open up the machine and look for the oil filler.