Full Idea
To trace something unknown back to something known is alleviating, soothing, gratifying and gives moreover a feeling of power. ...First principle: any explanation is better than none. ...Proof by pleasure ('by potency') as criterion of truth.
Gist of Idea
Any explanation will be accepted as true if it gives pleasure and a feeling of power
Source
Friedrich Nietzsche (Twilight of the Idols [1889], 5.5)
Book Reference
Nietzsche,Friedrich: 'Twilight of the Idols and The Anti-Christ', ed/tr. Hollingdale,R.J. [Penguin 1972], p.51
A Reaction
By 'proof by pleasure' he means that we find an explanation so satisfying that we cling to it. I assume it is a criterion of rationality (an epistemic virtue) to reject the principle 'any explanation is better than none'. Negative capability.