According to Osho, Krishna is called a complete incarnation because he is totally empty—egoless and choiceless. Emptiness is indivisible like zero; therefore it alone is whole. By refusing any fixed identity or 'somebodiness,' Krishna is nothing and thus can be all. When Arjuna asks who he is, Krishna doesn’t define himself; he reveals the total, illustrating that wholeness flowers from utter emptiness.
When you drop every label and choice and become like a zero, nothing limits you—so, like Krishna, you can include everything.