Also he could set up a three column chart.
First column name of assignment, second...rating 1-10 how much I think I will like the assignment, third...rating on how much I actually enjoyed assignment.
After a while he might see he over estimate how bad something might be and in actuality it will probably be tolerable to fun...with the occasional no fun assignment. Then you can convince him to start at least assuming the assignment will be fine to enjoyable from the beginning and skip the negativity. Because the data supports being positive.
