How can one figure out ultimate truth, if simple truth remains in doubt?
What is truth? Truth is the state of being true.
Being true is the great mystery.
Being true is being transparent, so that what is real is visible, and not hidden.
As an analogy, a mother giving birth is a mother being transparent. The reality of the baby is made visible via the mother.
A mother is made possible via love.
Love is the great mystery. Love is transparent. Love is truth.