Full Idea
My reports on myself are subject to the same kinds of defects as are my reports on you.
Gist of Idea
Reporting on myself has the same problems as reporting on you
Source
Gilbert Ryle (The Concept of Mind [1949], Ch.6)
Book Reference
Ryle,Gilbert: 'The Concept of Mind' [Penguin 1949], p.185
A Reaction
This may be true of memories or of motives, but it hardly seems to apply to being in pain, where you might be totally lying, where the worst I could do to myself is exaggerate. "You're fine; how am I?"