"It will not be we who reach Alpha Centauri, and the other nearby stars, it will be a species very like us, but with more of our strengths and fewer of our weaknesses, more confident, far-seeing, capable, and prudent. For all our failings, despite our limitations and fallibilities, we humans are capable of greatness."-Carl Sagan
Imagine how different the outcome of the Covenant-Human war be if Truth said yes to that?
They would have most certainly glassed Earth and wiped out Humanity.