There was this philosophy professor in a prestigious university who loved to teach students about important theories of the subject. Once, while his lecture was about to begin, he just closed the book and instead stood before his class with some items on the table in front of him. Students were curious but the professor without looking at them silently picked up a very large and empty mayonnaise jar. Thereafter, he started to fill it with small rocks. Once the jar appeared full, professor proceeded to ask his students ‘whether the jar was full?’