The short version is that the work to produce the "next" block depends on the previous block. The moment a new block is found, any in-progress searching is aborted because it won't produce anything useful. This is important because it encourages a "found" block to be used and distributed quickly.
You should see this message each time the bitcoin network as a whole finds a new block.
Thank you.
Does it has any influence for the efficiency of mining? I found seems the increase speed of "accepted" reduced when this phrase appear over and over. (Is the psychological effect to me?)