Each of us should know what we consider to be greatness in ourselves, and we should cultivate that. If each of us makes strides to be great in our own right, we will be greater collectively. What is "great" to you can be different than what is "great" to me, so long as our ideas of "greatness" do not include harming others or discouraging greatness in others, no matter what form it takes.
A baby taking her first steps is achieving greatness. A man walking on the moon is achieving greatness. Can we all agree that it is the pursuit that is important, not the final outcome?