The phrase their observance is essential to the definition. A person may memorize a rule of inference yet misapply it in an argument. In that case, knowledge of the rule has not achieved its intended benefit.
Example: Understanding that “Every human is an animal” does not imply “Every animal is human” is one thing. Making that reverse inference in discussion is a failure to observe the rule.
Thus the protective effect of logic depends on actually using the rule correctly. Memorizing its terminology alone is insufficient.