Cat
The domestic cat presents itself as a readily accessible phenomenon for those willing to accept its terms. Cats may be acquired through breeders, shelters, or the time-honoured tradition of simply appearing at one's door and refusing to leave. Once installed, the cat remains perpetually accessible—indeed, often excessively so, particularly at mealtimes or whenever the human attempts to use a keyboard. Access to one's cat is limited only by the cat's own schedule, which may or may not align with human preferences.
Rainbow
Rainbow accessibility operates under entirely different parameters. The phenomenon requires specific atmospheric conditions: rain or mist combined with sunlight at an angle of approximately 42 degrees from the observer's shadow. One cannot summon a rainbow through desire alone; one must wait for meteorological cooperation. The average rainbow persists for merely one hour under optimal conditions, and many last mere minutes. Those residing in arid climates may wait months between sightings. The rainbow does not come when called.