Data! Evidence!
Heinlein said it well:
What are the facts? Again and again and again - what are the facts? Shun wishful thinking, ignore divine revelation, forget what 'the stars foretell,' avoid opinion, care not what the neighbors think, never mind the unguessable 'verdict of history' -- what are the facts, and to how many decimal places? You pilot always into an unknown future; facts are your only clue. Get the facts!Robert A. Heinlein, Time Enough for Love, 1973
GREAT!! ANSWER!!! The same one I use for my belief in the Bible.