An elderly man asked me if I could calculate the population in the year 2020 if today it is X and it grows at an exponential rate of t. Easy enough, I whipped out the calc book and showed him the formulas for exponential growth: e to the tX.
But he wanted me to derive the e. Sorry, I don't know. I can't call Euler either...
It's like asking why is pi 22/7. However, I do admire the guy for wondering.