Yeah,
The problem for me is that when you have to look at the backside of the folded object - fold the object and rotate it around. For example, like on this problem:
http://img180.imageshack.us/f/32684450.jpg
My brain cannot hold the image and rotate it. I mean, I am having trouble even getting the edges connected. Do you fold the image in your head then rotate it? Or do you use techniques, like for TFE where you can count lines?