Right now, it doesn't make sense to me. It says: Strong Pareto Optimum is "a movement from one allocation to another that can make at least one individual better off" and a "Weak Pareto Optimum (WPO) satisfies a less stringent requirement, in which a new allocation is only considered to be a Pareto improvement if it is strictly preferred by all individuals". Surely being strictly preferred by all individuals is a more stringent outcome than being strictly preferred by one individual? Or am I misunderstanding what strictly preferred means?