The big thing is the scientific process. Go through the steps and if the hypothesis is wrong -- do a little more research and try to explain why it was wrong.
My son did a pickle light one year and then tried other fruits and vegetables to see if they would light up, this one won an award because his hypothesis was wrong, but he found out why he was wrong.

In one of my college classes, we were talking off topic about how coffee helps plants grow better and someone wondered if altern in coffee would affect it or sugar for that matter.