This fixed-brain notion begat a host of homespun clichés and conventional wisdom to the effect that you simply cannot teach an old dog, or even a middle-aged dog, new tricks; that from age thirty the leopard does not change its spots, that you are who you are and you better get used to it because no amount of therapy, life experience, or other magic can make a significant dent in the architecture of your brain or your personality, except by changing it for the worse, through disease, stroke, cancer, poisons, alcohol, drugs, or dementia.
