The Second Guideline of Temporal Communication, should you happen to find yourself in the position (possible, albeit rare outside navigational errors, advanced relativistics classes, and other esoteric situations) of being the subject of a closed timelike curve formed by the appropriate combination of wormhole traversals and near-luminal travel, or alternatively should you find yourself in the much less likely position of having access to a trans-temporal ansible without being an acausal-logic-using temporally-transcendent seed AI, is traditionally given as follows:
“Listen to your future selves, and politely fulfill whatever requests they have of you. They’ve been you; by definition, they know everything you know, have experienced everything you’ve experienced, and then have learned more on top of that. They know better.”
In practice, it’s not as vital as this makes it sound; the Chronological Consistency Protection Theorem tells us that global causality is always preserved, and that while effects may precede their causes locally, nonetheless the causal graph is always complete. Even if you choose to ignore or defy your future self, you cannot damage the fabric of causality by doing so.
The corollary to this, of course, is that it doesn’t matter. Your future self knows exactly what you will do in response to any interactions you may have, because they were you when they had them the first time around. It follows, therefore, that they always say and do exactly the things required to cause you to do whatever you are going to do to cause the timeline that resulted in the encounter you are now having in the first place.
The Second Guideline, therefore, does not exist to protect the integrity of the temporal continuum; merely to prevent a lot of pointless and futile arguing with oneselves.
– Practical Temporal Mechanics for Amateurs