Just how different can each person get? And just what constitutes stealing other writers' ideas? As some of you may have seen on my blog I felt I was doing just that when I chose to write about depression. But then, that's something different people face differently. That, I learned, is how someone shows their own voice. This is how writers are unique. Some things are bound to be similar in different works, but each one stands out from the author's voice. I'm sure everyone will agree with this.
Also, I sometimes ask myself what expressions can be considered cliched. My memoir writing instructor said "the nail in the coffin" is an example of a cliche, which should be avoided in memoirs. I asked once on my blog once if "making big deal out of nothing" sounds cliched (I used that one in the memoir).
I try hard enough to make my story sound like my own ideas, even if they have been used before.