I'm neither at the beginning of it, nor at the end of it, however without me life would just be incomplete.
This is a logical riddle.
I see the question was already answered correctly by C.Woods, but I was going to say
The middle, as in the middle of life itself, rather than the actual word. It's not the beginning or the end however without the middle, life would just be incomplete. It ended up being the middle of the actual word "life"
My first thought was...
the 'F' letter: not at beginning or end, but without it LIFE is incomplete (it is a LIE). On second thought, there is also the F word: not at the beginning (too young) or end (too old!), but without it life is incomplete (get a LIFE!). Actually, without it there would be no life at all.
Now don't ask me why people in France call it "la petite mort" (the small death)...