Full Idea
Work out who is most oppressed and disadvantaged in the situation, and then adopt their version of events as the right one. If something is not true in the eyes of the least favoured, then it is not true.
Gist of Idea
The truth about events always comes from the oppressed and disadvantaged
Source
report of Jean-Paul Sartre (The Communists and Peace [1953], final part) by Sarah Bakewell - At the Existentialist Café 12
A Reaction
A theory of social truth, rather than truth in general. A bit simplistic, but appealing. If you want to know the truth, ask the people involved. This is true of the Savoy Grill, as well as of homeless life. You must first care about the oppressed.
Book Reference
Bakewell,Sarah: 'At the Existentialist Café' [Chatto and Windus 2016], p.271