Pleas allow me to quote André Weil twice. First, from page 27 of *The Apprenticeship of a Mathematician*, concerning his first form teacher, Monsieur Collin:

'There was a strong temptation to take short-cuts, saying "it is obvious that..."; Monsieur Collin taught me never to use this word. "If it were obvious," he said, "you would not feel the need to say so; if you say so, that means it is not obvious." He is the one who taught me how to write up mathematics.'

The second quote, from page 19 of *Elliptic Functions According to Eisenstein and Kronecker*:

"Combining the above formulas, we get for all $n\geq 1$, the following series for $E_n(x)$:
$$E_n(x) = u^{-n} \sum_{v=-N}^{+N}\epsilon_n(\zeta + v\tau)+\frac{(2\pi/iu)^n}{(n-1)!}\sum_{v=N+1}^{+\infty}\sum_{d=1}^{+\infty}d^{n-1}q^{vd}[z^d+(-1)^nz^{-d}]$$
where the double series is easily seen to be absolutely convergent provided $N$ has been taken such that $|q^{N+1}z|<1$ and $|q^{N+1}z^{-1}|<1$."


I will refrain from the obligatory *of course* joke and leave the moral of the story as an exercise instead.