But in the scenario you propose, the fact that some people with the same exposure to the world are not as susceptible to the conditioning suggests that some brains differ from others to begin with, in ways that are important to how we interact with the world. This would fit well with what is called the diathesis-stress model. https://medium.com/wise-well/one-grand-factor-aims-to-explain-all-mental-health-conditions-8d549d87445c