The reason behind this fear is that up until they learned about fractions everything was counting. If you broke a cookie into 5 parts then the students were told that there was 5 pieces. Now they also have to understand that each piece is worth 1/5 of the whole thing, which is really weird for them.

How would you help the students get past this weirdness that something can be a part of something else? This is harder than it sounds!