The concept of the pigeonhole principle in simple noding terms:

If there are A nodes and B writeups that exist within the A nodes, where A>0, B>0, and A<B, then at least one node contains more than one writeup.

Suppose you have 51 nodes, and those nodes have id numbers between 100000 and 100099 inclusive. The pigeonhole principle can prove that at least two of your nodes must have id numbers that are consecutive integers (without having to spam Everything with a bunch of useless nodes).