What is a trial court's duty to instruct a jury on the general principles of law applicable to the case?

"Even absent a request, the trial court must instruct on the general principles of law applicable to the case. [Citation.] The general principles of law governing a case are those that are commonly connected with the facts adduced at trial and that are necessary for the jury's understanding of the case." (People v. Young (2005) 34 Cal.4th 1149, 1200.) "[T]his duty ... extends to defenses 'if it appears ... the defendant is relying on such a defense, or if there is substantial evidence supportive of such a defense and the defense is not inconsistent with the defendant's theory of the case.' " (People v. Brooks (2017) 3 Cal.5th 1, 73.)