Why is a pyramid of numbers not always a good example of the flow of energy through a food chain? i really don't get this. can anyone explain?

The pyramid of numbers only compares the number of organisms present in each trophic level at A PARTICULAR TIME. This pyramid can be inverted if organisms of one trophic lvl is parasitic on organisms of another trophic lvl. or when threre are many small organisms feeding of one trophic level feeding on a large organism of anoyher trophic lvl.
For eg. tree→aphid →protozoa, the pyramid of numbers is upside down
however pyramid of energy is always in a pyramid shaped as it compares the total energy in each trophic level OVER A PERIOD OF TIME. more energy is lost when we mive along a food chain hence the shape is ALWAYS pyramid.