I was just setting up a Website, and after a few hours oft work, it was done and working absolutely fine. So proudly I presented it to my customer, who then said something like: "Okay, but why is there all this weird serif font thing without any graphics going on?"
I searched the whole code of the page and the CSS, haven't found any mistake. all the files were also where they should be. After more than a week and a few mails form an unhappy customer, I found the problem by accident: I just used the folder name "assts" instead oft "assets".
Since then, I always note which file or folder I rename.