... A rule of thinking which would absolutely prevent me from acknowledging certain kinds of truth if those ... truths were really there, would be an irrational rule.
William JamesThe sovereign voluntary path to cheerfulness, if our spontaneous cheerfulness be lost, is to sit up cheerfully, to look round cheerfully, and to act and speak as if cheerfulness were already there. If such conduct does not make you soon feel cheerful, nothing else on that occasion can.
William James