The calculation for the electron positron annihilation to 2 photons amplitude takes up 5 pages in $\LaTeX$, and the answer is astonishingly simple
Even Griffiths notes this quite sarcastically in his book. Is there a deeper reason that the machinery of QED makes this simple process so hard to calculate? Does it have something to do with gauge fixing and the complications that it brings? Is there a slick way to come to this simple answer by utilizing certain tricks and symmetries?