“Endgaining” means being so focused on results of your actions, or “gaining your ends” — that you do not stop to give due consideration to the means by which you gain your ends. Conversely, “non-endgaining” is shorthand for deciding, and then carrying out the decision, to not give into this habitual rushed or lazy habit of thinking, and to take time and consider how to best get from point A to point B. As they say, “A stitch in time saves nine” and this applies to simple actions like standing up out of a chair as well as to year-term complex goals like learning a language.
Basically, “endgaining” means that you are so focused on the end, that you do not stop to consider the means by which you reach your end. If your “end” is to stand up out of a chair, are you able to stop and consider how can do so without scrunching and putting undue strain on your joints? The Alexander Technique teaches a practical technique to stop, free yourself from a fixed (and usually unconscious) notion of how to achieve something, and consider how you approach a problem in a more rational manner. Give yourself time. Come back when this article is done!