Cat
The cat's reliability operates on its own terms entirely. It will be present when it chooses to be present. It will provide comfort when comfort aligns with its current objectives. A cat may spend three hours upon one's lap one day and avoid all human contact the next, offering no explanation for either behaviour. The cat is reliably unreliable—one can depend upon it to defy prediction with remarkable consistency. Its presence is guaranteed; its cooperation is not.
Silence
Silence, when achieved, delivers exactly what it promises: nothing. There are no variables, no mood fluctuations, no mysterious 3 AM energy bursts. Silence does not knock objects from shelves, vomit on carpets, or demand feeding at inconvenient hours. Its reliability is absolute and unchanging—the problem lies entirely in achieving it. Once obtained, silence performs its function with perfect consistency. The challenge is that obtaining it requires either extreme isolation or complete deafness.