What does "handle" mean in this context?

Question

The context comes from the movie "Fear And Loathing In Las Vegas" It's a scene in which the main character describes the 1960s

        THERE WAS MADNESS IN ANY DIRECTION,
        AT ANY HOUR... YOU COULD STRIKE
        SPARKS ANYWHERE.  THERE WAS A
        FANTASTIC UNIVERSAL SENSE THAT
        WHATEVER WE WERE DOING WAS RIGHT,
        THAT WE WERE WINNING.  AND THAT, I
        THINK, WAS THE **HANDLE** -- THAT SENSE
        OF INEVITABLE VICTORY OVER THE
        FORCES OF OLD AND EVIL.  NOT IN ANY
        MEAN OR MILITARY SENSE; WE DIDN'T
        NEED THAT.  OUR ENERGY WOULD SIMPLY
        prevail.  We had all the momentum;
        we were riding the crest of a high
        and beautiful wave...

"handle" noun: : a means of understanding or controlling can't quite get a handle on things(source merriam webster)

Is this the correct def?

Answer 1

A number of figures of speech involve the hands. If we hold an understanding of something we can say that we 'grasp' it; If we wish to control or understand something we can say that we wish to 'get a grip' on it. A handle is something that we can use to hold or control something, and thus the figurative usage that you have found arises.