Soft 404
2 facts:
in Russian, the 3-legged thingy is called stool too
We call a chair stoel in Belgium and Netherlands, Stuhl in German.
Now you, Englishmen 
Somebody put some effort into that sketch...
Maybe a cutty stool or a milking stool, but in this (non-stool) case it is usually called "the three pillars".
In my case the 3 pillars are: external knowledge (Google etc.), internal knowledge, ingenuity (extracting useful knowledge to formulate a solution). Sometimes I can stand on just two legs...