Orthogonal Functions: Questioning the Reason Why

[Logarythmic]

A question for my understanding:

If I have an operator $$\cal{L}$$ and a set of eigenfunctions $$\phi_n$$ of this operator, then the eigenfunctions are orthogonal. Why is that?

 

[OlderDan]

A question for my understanding:

If I have an operator $$\cal{L}$$ and a set of eigenfunctions $$\phi_n$$ of this operator, then the eigenfunctions are orthogonal. Why is that?

Here is a short read on this issue.

http://vergil.chemistry.gatech.edu/notes/quantrev/node16.html