Sometimes when you design things you become blind to the fact that your graphical design does not actually work all that well. It can happen that you fail to account for some corner case or you can fail to account for missing contextual information etc.
How do you ensure you are in fact designing it right and the design works as intended? When doing some user testing how do you ensure you do not taint the test with your context that then does not always exist? Or we might ask teh wrong audience. What other options do we have?
Image 1: Sometimes you just don't get the design as presented.
Both of the designs above probably were perfectly valid in environment where they were designed, just not when they were applied. It is just that the selection highlight probably worked quite well when the designed menu had more than 2 items. Well tough luck in the version i was presented they weren't present. Likewise the symbol if perfectly understandable if you happen to see its counterpart, but alone it does not work as well. Unfortunately in practice this comes up every day since the icon are not all next to each other.