Dr. Benny Brown wrote:
... rules are standards that determine the normative status of concrete actions, while principles determine goals that the actions are supposed to achieve.15 A person cannot perform two conflicting actions, but he can undertake different goals that may be found in conflict in particular circumstances, and nevertheless not forego any of them. These goals may be more abstract (such as ‘‘justice’’) or less abstract (such as that ‘‘no man may profit from his own wrong’’).
Yeshayahu Tishbi and Joseph Dan wrote similarly regarding the relationship between halakhah and musar: ‘‘The halakhah cuts to the minimum that the servant of God is required to do in order to fulfill his obligation to his Creator [...] The musar literature seeks not the minimum, but the maximum – the path by which man will reach the zenith of religious life, of approaching and clinging to God.’’21
Maharal (Be’er HaGolah #6): One does not always accept the literal meaning of Agada as our Sages said, “that one does not resolve apparent contradictions in Agada.” That is because it is possible that the idea of the Agada was said in a concealed manner. Therefore, there is no need to ask or resolve contradictions in Agada since by apparently clarifying one Agada a contradiction to a different Agada can be created. It is possible that the original problem was not a problem to those who understand their esoteric nature. In contrast, Halacha cannot be utilized without resolving all apparent contradictions and inconsistencies. Agada on the other hand was not created for the purpose of learning what is prohibited or permitted and therefore consistency is not required. By attempting to create consistency it is possible that problematic elements will be rejected when in fact there was never a problem in the first place to those who are experts in Agada. That is why the Yerushalmi (Peah 2:4) states that one should not learn Halacha from Agada - since it has not been conceptually clarified by the dialectic process of questions and answers…
Nodah BeYehuda (161): Even though the Yerushalmi (Peah 2:4) equates not learning practical Halacha from Mishna, Tosefta and Agada - the reason is not the same for the three. … Medrash and Agada were composed entirely for the purpose of teaching moral lessons by means of allusions and allegories. Thus, they are the source of theological information but were never intended to be used for Halacha. That is why we do not learn at all from Agada to decide practical Halacha.
Consequently problems are created when taking mussar and agada and viewing it as halacha - as we see concerning bein adam l'chavero issues such as lashon harah or tznius.