What arguments are there to support a statement 'the goal of life is to be able to express yourself as entirely and truthfully as possible'?

I'm not familiar with arguments concerned with such a goal, per se. But many philosophers have argued for the importance of something you might regard as related to truthful and complete expression--namely "authenticity." Authenticity might be defined as taking responsibility for what one is and perhaps also affirming it, perhaps affirming it publicly.

The use of ‘authenticity’ as a critical term is associated primarily with existentialist philosophers like Jean-Paul Sartre and Simon de Beauvoir. Sartre’s and Beauvoir’s conception however was drawn from the work of phenomenologist Martin Heidegger (who is also, unfortunately, sometimes categorized as an existentialist), especially Sein und Zeit [Being and Time] (1927).

Arguments in favor of being authentic seem to reliy on the premise that life is somehow more meaningful when lived authentically.

Some philosophers have also made appeal to a kind of aesthetic view of life, such that realizing a beautiful self or treating one's life as a work of art (expression) leads to happiness, fulfillment and meaning.

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