A chair comprising a seat and a seat back made of non-resilient materials, in which - the seat has a shape that matches the natural contours of an occupant's buttocks, thighs, and upper legs, wherein - the seat's concave backward portion (205a, 205b) is connected to the concave lowest portion of the said seat back, creating a dedicated concave zone that contours the occupant's buttocks closely; - the seat's concave backward portion (205a, 205b) has in its center a small hump that contours tightly an occupant's sacrum and coccyx if his buttocks are fitting inside the dedicated concave zone; - the seat's forward portion has a wide W-shape that contours the occupant's upper legs, wherein the two concave zones (202a, 202b) of the seat's W-shaped forward portion contours the back sides of the occupant's upper legs, and the very center zone of the seat's W-shaped forward portion is convex and snuggles the occupant's thighs; - the seat is inclined backwardly in such a way that, when the occupant intentionally sits on the forward portion of the said seat, his buttocks, pushed by the gravity force of his body, will gradually glide backward and fit themselves into the said dedicated concave zone eventually; - the left side and right side (203a, 203b) of the seat's W-shaped forward portion are convex so that they contour the outer sides of the occupant's upper legs; - the seat back tilts backward to stay at an angle of 135 degrees to the seat and contours the occupant's back, wherein - the seat back's lowest portion is concave to contour the occupant's buttocks; - the middle portion is convex to contour the lumbar vertebrae; - the upper portion is concave to contour the thoracic vertebrae; - the top is a headrest to provide support to the occupant's head; and - the left and right edges (304a, 304b) of the seat back are convex so that the occupant's back cannot bend left or right. - the seat has a shape that matches the natural contours of an occupant's buttocks, thighs, and upper legs, wherein - the seat's concave backward portion (205a, 205b) is connected to the concave lowest portion of the said seat back, creating a dedicated concave zone that contours the occupant's buttocks closely; - the seat's concave backward portion (205a, 205b) has in its center a small hump that contours tightly an occupant's sacrum and coccyx if his buttocks are fitting inside the dedicated concave zone; - the seat's forward portion has a wide W-shape that contours the occupant's upper legs, wherein the two concave zones (202a, 202b) of the seat's W-shaped forward portion contours the back sides of the occupant's upper legs, and the very center zone of the seat's W-shaped forward portion is convex and snuggles the occupant's thighs; - the seat is inclined backwardly in such a way that, when the occupant intentionally sits on the forward portion of the said seat, his buttocks, pushed by the gravity force of his body, will gradually glide backward and fit themselves into the said dedicated concave zone eventually; - the left side and right side (203a, 203b) of the seat's W-shaped forward portion are convex so that they contour the outer sides of the occupant's upper legs; - the seat back tilts backward to stay at an angle of 135 degrees to the seat and contours the occupant's back, wherein - the seat back's lowest portion is concave to contour the occupant's buttocks; - the middle portion is convex to contour the lumbar vertebrae; - the upper portion is concave to contour the thoracic vertebrae; - the top is a headrest to provide support to the occupant's head; and - the left and right edges (304a, 304b) of the seat back are convex so that the occupant's back cannot bend left or right.