"Most successes are unhappy. That's why they are successes - they have to reassure themselves about themselves by achieving something that the world will notice"

This quote by Agatha Christie recommends that lots of successes are driven by a need to be observed and validated by the world. It implies that those who succeed frequently have an underlying misery that they are trying to fill by accomplishing something that will be discovered and valued by others. This might be an outcome of an absence of self-esteem or a feeling of emptiness that can only be filled by external recognition. It recommends that success is frequently a way of trying to make up for an absence of internal fulfillment. This quote implies that success is typically a way of trying to fill a psychological void, instead of a genuine desire to achieve something.