Hasn't it all been said before?

No. Everything is actually amazingly new:

[D]on't people accidentally repeat each other's sentences all the time? It seems to me that this should not be unusual. Yet try plugging that last sentence word by word into Google Book Search, and watch what happens.

It: Rejected—too many hits to count
It seems: 11,160,000 matches
It seems to: 3,050,000
It seems to me: 1,580,000
It seems to me that: 844,000
It seems to me that this: 29,700
It seems to me that this should: 237
It seems to me that this should not: 20
It seems to me that this should not be: 9
It seems to me that this should not be unusual: 0

It seems to me that this should not be unusual is itself ... unusual.

(From an article on catching plagiarists.)