A healthy condition of tiredness doesn’t have to prevent us from carrying out concentration and meditation with great willpower. On the contrary. Nature does one part of the work for us, since it dulls the outer sense organs and lessens our ability to take in sense impressions. For the goal is to see without physical eyes, to hear without physical ears and to think without a physical brain. It’s precisely when we are tired that we can illumine and warm our being with the luminous thoughts of meditation.
Source: Rudolf Steiner – GA 266 – From the Contents of Esoteric Classes: Esoteric Lessons – Part II: Cologne, May 9, 1912