Tamas
तमस् (tamas)
The strand of inertia - heaviness, dullness, and concealment; the ground of rest and the swamp of avoidance.
Tamas is darkness and mass: the guna of stillness, sleep, forgetting, and form. It has the worst reputation of the three and does not entirely deserve it - without tamas nothing holds shape, and no one sleeps. It is inertia in both senses: stability and stuckness.
Its shadow forms are recognisable - the fog that calls itself tiredness but is really avoidance, the cynicism that spares one the effort of hope, the scroll at midnight. Tamas conceals; its favourite concealment is itself.
The classical remedy is not sattva directly but rajas first: movement breaks inertia, then clarity can follow. Hence the old advice that when you cannot meditate, walk; when you cannot walk, stand; light one lamp rather than cursing the dark you are made of.