Aristotle's distinctions among types of causes are, I think, very useful compared to root cause analysis. It's not that some why's are more important than others in an absolute sense. Rather than having four different "why?" questions one after the other, he pointed out there are four kinds of "why?" you can ask simultaneously, and depending on what your needs are one may be more important than another at a given time.

So, for "why is the table flat?", the four causes are:

1. (Material cause) because it is made of wood, and wood is rigid, and so holds its shape.

2. (Efficient cause) because a carpenter took a plane or chisel and cut away all the wood that wasn't the flat surface.

3. (Formal cause) because the blueprint the carpenter used was of a flat rigid surface suspended over 4 legs.

4. (Final cause) because if it were not flat, your jug of wine would fall over when you set it down on it.

This is in some ways superficially similar to the "five why's", but it is more flexible, because you do not have to go in that order. You might look at two tables and ask why this one is flat and this other one is curved, and realize that it's because this other one is made of canvas rather than wood, and the canvas has started sagging. This framework also lets you categorize each type of "because" as you receive it.