A more thorough explanation:

Definition: The phrase sine qua non is Latin for “without which not.” When something is described as sine qua non, it is a necessary or indispensable requirement. The phrase represents an essential element, component, or condition of something else.

For example, in order to be a successful athlete, regular training is a sine qua non. Without consistent training, an athlete cannot improve their skills and performance.

Another example is that good communication is a sine qua non for a healthy relationship. Without open and honest communication, misunderstandings and conflicts can arise.

These examples illustrate how sine qua non refers to something that is crucial and cannot be done without. It is an essential part of achieving a certain goal or outcome.