Where does the term Armchair Psychologist come from? I understand it means someone who has no formal training who 'sits in their comfortable armchair' and gives (usually) unsolicited advice to others, but where does this expression come from? When was it first used, etc.? Also, why an "armchair"? Wouldn't a psychologist usually be sitting in an armchair when they're giving an analysis?
The oldest of these expressions seems to be arm-chair traveller in 1809, at least according to OED. OED also provides a good definition for the expression that explains why "armchair" is significant:
Based or taking place in the home as opposed to the world or environment outside; amateur, non-professional; (hence) lacking or not involving practical or direct experience of a particular subject or activity. Also: comfortable, gentle, easy.
An armchair stands out from other kinds of chair in that it has arms for additional comfort, and one ordinarily sits in one at home as opposed to the workplace. My desk chair at the office has arms, but it is no armchair. The psychotherapists I see on TV do not sit in armchairs, but ordinary office chairs, or at least, chairs which are not primarily intended for lounging in.
Thus, an armchair professional is one who is an amateur, or otherwise has no professional experience— or responsibility— regarding the opinions s/he is sharing.
The sense is more than two centuries old; the OED finds an entry in the September 1809 The Monthly Review:
A great portion of this volume is ocupied by a description of Edinburgh; which, while it instructs the arm-chair traveller, must be highly satisfactory to the Scottish nation.
Armchair critic is attested from 1856, armchair strategist from 1888, armchair general from 1900, and armchair quarterback from 1932.