Like you suggested, the most useful thing is the 'For fuck's sake, don't be Gamma!" motto. Vox's system plus The Last Psychiatrist's description of narcissism made me finally feel what Gamma
is - which helped me stop being that.
A friend of mine who went through something similar said, "I suddenly felt just how much energy I was devoting to controlling other people's impressions of me. And I realized that I could do pretty much anything if I channeled this energy into anything useful."
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Second in the usefulness scale is being able to smell Gamma in others. To me, Gamma is mostly "overreach". Saying a rare personal opinion as if it were 90+% believed in, or having strong conclusions regarding a subject you haven't studied, are Gamma behaviors. If you recognize Gamma as Gamma, you'll challenge the competency of the speaker, rather than the truth of their conclusion, and make them quickly quit on frustration. Once the Gammas flee, you'll get a much more intelligent conversation.
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This last one I haven't extensively tried, but it may be the most useful of all: Weaponize Gamma thinking against other Gammas.
Dusty's thread on Albert Ellis's "A Guide to Rational Living" is under-rated gold. People who love that thread apply its ideas to make themselves and their loved ones more healthy and happy.
True shitlords use its ideas to magnify the insecurities of those who disagree with you politically.
Weaponized Gamma knows what a Gamma would think in any situation, and injects those Gamma thoughts into someone else, to utterly demoralize them. Frightening, but I've no qualms doing this to SJWs.
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Sorry I didn't answer your question directly, but you can average your own behavior over many situations to say, "I'm a Delta."