The ripening hormone
Ethylene is the plant hormone that coordinates ripening — fruits produce it as they mature, and it triggers neighboring produce to ripen (or age) too. Producers: bananas, apples, tomatoes, avocados, stone fruit. Sensitive victims: leafy greens, carrots, cucumbers, broccoli, peppers.
The deliberate uses
Paper bag + banana = rock-hard avocados ripe in 24–48 hours. Paper bag + apple = peaches that soften. The rice-buried trick for mangoes works on the same principle. Ethylene is a tool: aim it at what needs ripening and shield everything else.
The accidental waste
The mixed fruit bowl is an ethylene exchange chamber; the shared crisper drawer is worse (concentrated). One apple beside the lettuce browns it overnight; tomatoes beside cucumbers yellow them in days. The geography fix: producers in one zone (or hanging), sensitive items in the crisper, and the fruit bowl reserved for ready-to-eat only.