From मनुस्मृति
देवे तीर्थे द्विजे वैद्ये बुद्धिर्भवति यादृशी |
यादृशी भावना तत्र सिद्धिर्भवति तादृशी ||
This श्लोक: is an interesting take on belief. It articulates that results obtained from God, Pilgrimage, Brahmin, Doctor are directly proportional to the belief in them !!