The referent of anaphora is not always obvious.
Example:
The investigators discovered that the researchers had
falsified their results. This means
that they would have to submit . . .
Notice that in the above example, the idea that this
refers to is still not clear for seven words after it is used;
this could refer to the
fact that the researchers falsified their results, or this could refer to the
fact that the investigators discovered the falsified results.