Miller's Law can refer to three different principles.
Miller's law, part of his theory of communication, was formulated by George Miller, Princeton Professor and psychologist.
It instructs us to suspend judgment about what someone is saying so we can first understand them without imbuing their message with our own personal interpretations.
The point is not to blindly accept what people say, but to do a better job of listening for understanding. "Imagining what it could be true of" is another way of saying to consider the consequences of the truth, but to also think about what must be true for the speaker's "truth" to make sense.
In software development
Miller's Law was formulated by Mike Beltzner and is named in respect of Dave Miller, long-standing owner of the Bugzilla product:
"All discussions of incremental updates to Bugzilla will eventually trend towards proposals for large scale redesigns or feature additions or replacements for Bugzilla."