This is not something which we know to be true. Pi is thought to be a [normal
number](https://en.wikipedia.org/wiki/Normal_number) but there is no proof of this.
It almost certainly is though.
> akshually, this is true of any irrational number, not just pi
This is not true of all irrational numbers. For example, the number 0.1010010001..
is irrational but does not contain the sequence '11' in its expansion.