

You can also say " Is this/that it?" if you are not satisfied with how someone finished some task: Is this (that is in front of us) it (the it that we agreed and shook hands on)?

Taking RiMMER's examples - the it is waiting for the results and waiting for the painter in both cases the statement means the wait is over (it ends) or about to finish. It denotes that that it does not extend beyond this - in this way it is associated with the end. In another words, the key is it and the fact that that it is equal to this that we have, see, experience. " This", as in this that you perceive and you are aware of, " is it", where " it" is a third person pronoun, refers to some " it" that is already known to the writer and the reader or the talker and listener (something that was discussed or agreed upon earlier or something that is clear from context).
