It has always been fascinating to observe how people can behave so differently. Why do we do this? We all spontaneously engage in many different behaviours and I assert that we continue to engage in those behaviours because of the reinforcement that we receive. Reinforcement can take many forms and can be from many sources. A parent hugging a child who begins to walk, encouraging every movement towards their success, is one example of successful selective reinforcement. A child learning that if they misbehave their parents stop fighting with each other is another. Past reinforced behaviours will change the likelihood of other spontaneous behaviours being reinforced – or even presented at all – in the future, leading to widely differing outcomes resultant from only minor differences in the initial reinforcement.