How is the LES damaged?

I read someone say they had put there LES under too much stress over
the years and it had given up.  Does this mean for example eating too
much steak, lying on your bed instead of sitting upright etc and then
over the years this pu****ng up of the acid weakened the LES?

Also my ENT doctor looked down my throat with a  camera, but couldnt
go too far, am i right in saying that it isnt the LES which stops his
camera going any further but the other valve.  The LES is another
valve further down and right?

Just trying to understand the anatomy of it all.