This reminds me of my early C days dilemma: "Check for a disallowed NULL pointer argument on function entry or just trust that it will have a valid value?" And

This reminds me of my early C days dilemma: "Check for a disallowed NULL pointer argument on function entry or just trust that it will have a valid value?" And a mixed feeling that would settle after putting an assert there. Eventually, one develops a "pragmatic trust", appropriate to the level of interactions in the code. After all a state change is a kind of input resulting from an interaction. Some interactions are more trusted than others. Asserting reality after every handshake is not going to make one feeling safer. Operating in a trusted environment and understanding and upholding its premises does add one more member to enforce that "safety in [sane] numbers".