The word "精疲力尽" is formed through the combination of two parallel phrases: "精疲", where 精 refers to spirit or vitality and 疲 means weary, conveying mental or energetic exhaustion, and "力尽", where 力 denotes physical strength and 尽 indicates depleted, conveying physical depletion. These phrases are juxtaposed to emphasize a state of complete exhaustion.