"Time Management" and therbligs sounds like a very funny concept.
What you may not realize is it only sounds funny because we don't talk about it any more. We've been practicing Time Management for so long it's just a normal part of our life.
Time Management was not the normal way of life when the Gilbreth family was growing up. Society was converting from a mostly rural economy into an industrialized society.
Henry Ford's Model T wasn't the first car, it was just the first car that was mass-produced using production-line methods. The production line was a natural result of the move toward "Time Management."
Frederick Winslow Taylor is called the "Father of Scientific Management." Frank and Lillian studied Taylor's writing and theories, and supported them strongly. They knew Taylor personally, and Taylor publicly recognized their work in support of his own.
Unfortunately, Frank started to take his Time Management studies in a slightly different direction than Taylor's writings dictated. This lead to a break between Taylor's following and those who followed the Gilbreth's direction.
In one of the books, Frank Jr. and Ernestine talk about how the term Therbligs was coined. Frank was apparently taken by a story about a newspaper whose reporting was being stolen by rivals. The paper published a heart rending story about a ship named the Nelots what was sinking. Rival papers printed even more heart rending stories. Only then did the initial paper point out that Nelots was Stolen spelled backwards. Frank did the same with Therbligs. He coined the term (Gilbreth spelled backwards, mostly), and hoped that his now rivals the Taylorites would start using it and claim it was their own. Frank planned to dramatically illustrate that it was Gilbreth spelled backwards. Unfortunately, the plan backfired when one of the Taylorites noticed the spelling, and claimed that Frank was just using it to self-promote himself.
Time Management goes directly into Ergonomics. (That's a word we've all heard!) Lillian was studying that half a century ago.
Frank and Lillian's work has had a profound effect on the way we do things today!