To be fair, years ago, I was on a customer site implementing a custom mail routing program. I spent an hour looking at a line that was something similar to :
/* output route type. N=Rooty. P=Tooty */
fprintf(filey,"Route type %c\n",cRouteType);
It crashed. Over, and over again. Eventually after an hour I rubbed my eyes, looked at it again, and realised the line actually said :
fprintf(filey,"Route type %s\n",cRouteType);
I saw what I wanted to see for far too long before seeing what was actually there.