For the better part of a decade I worked as an actor, mostly summer stock and dinner theatre, but I actually got paid to pretend I was someone else. During those years, I worked with an assortment of other actors, many of whom were Method actors.
Method actors are an ongoing gift to the world from Constantin Sergeyevich Stanislavsky, an actor, writer, and director from Moscow who created an approach that forefronted the psychological and emotional aspects of acting. His technique came to be known as the Stanislavsky System, or "the Method."
Without boring you into a coma, I'll try to simplify what "the Method" is. It requires that, if an actor is to portray fear, he must remember something that terrified him and use that remembered fear to instill reality and credibility into his performance. The same with joy, lust, anger, confusion, etc. Stanislavsky's Method also requires that the actor know everything about the his or her character, usually by having the actor write a short "inner history" for their character, past details of their lives that -- while never used on stage -- would nonetheless give the performance even deeper authenticity.
In theory, Stanislavsky's Method is an amazing tool for an actor. It requires the complete submersion of the self into the body, psyche, and thoughts of another person so that an actor's performance rings true.
I use the phrase "in theory" above because, in my opinion, too many actors use Stanislavsky's Method as an excuse for self-indulgence masking itself as research.
Don't misunderstand -- when you get a Method actor like Marlon Brando (in his prime), Paul Newman, Dustin Hoffman, Sean Penn, Gregory Peck, Johnny Depp, Lance Henriksen, or Bob Hoskins (to name a small handful) who have the discipline and wherewithal to employ the Method to all its power, and you can have something glorious.
But I didn't get to work with any of them. I got to work with Method actors who would spend weeks researching and writing their "inner history", demand that I address them only as their character (even when off stage), and never, never make light of anything at any time.
The prime example of how Stanislavsky's Method can be turned into rampant silliness happened when I was doing a stage production of Sherlock Holmes and had to do several scenes with the actor playing Dr. Watson. (I played a slimy little safecracker named Sidney Prince.) The actor playing Watson had written a 25-page "inner history" for Watson, researched hand-to-hand combat methods used by British troops during the Boer War, studied medical procedures practiced in London in the 1800s ... and when the curtain rose each night, audiences were treated to his imitation of Nigel Bruce for two-and-a-half hours.
But that's not the silly part. The silly part always happened off stage, right before the third scene of the second act (where Watson confronts Prince). As he and I waited for our cues, the actor playing Watson would drink a cup of vinegar. I asked him why, and this, word for word, was his reply: "Because, Mr. Prince, dealing with you leaves a bad taste in my mouth."
Time to run, not walk, to the nearest exit.
I finally came to the conclusion that for me, as an actor, Stanislavsky's Method was useless. Every Method actor I had worked with wound up giving stiff, overly-mannered, obvious performances (in that it was obvious they were "acting"). I don't know that I'll ever do theatre again, but if I do, I'll use the same "technical" approach that I always used.
But I came to realize that, while Stanislavsky's Method might be useless to me as an actor, it was priceless to me as a writer. I still approach characterization -- especially during the early stages of a story or novel -- from a technical starting point, but almost always fall back on Stanislavsky's Method when it comes time to add emotional depth and authenticity to whichever character is coming to life on the page -- and I won't commit a single word to the page until said character is someone I recognize as an old friend.