What makes people make stupid mistakes like this one?

Yesterday at work my boss asked me to ask her son to bring a cushion for her back and when I went and asked her son for the cushion he brought out a small piece of sponge and told me that she uses that for a pain that she gets in her back. I actually took the sponge and carried it back to her and I was really embarrassed. Please give comments on this. Have any of you done anything so stupid before?