What is the duty of a court to instruct the jury on any lesser included offense to a charged crime?

Clearly it is the duty of a trial court to instruct the jury on any lesser included offenses to a charged crime when there is substantial evidence on which a rational jury could find the defendant committed the lesser crime, rather than the one charged. However, "'the existence of "any evidence, no matter how weak" will not justify instructions on a lesser included offense . . . .' [Citation.] Such instructions are required only where there is 'substantial evidence' from which a rational jury could conclude that the defendant committed the lesser offense, and that he is not guilty of the greater offense. [Citations.]" (People v. DePriest (2007) 42 Cal.4th 1, 50.) The crime of grand theft from a person (Pen. Code, 487, subd. (c)) is lesser to robbery and lacks the requirement of use of "force or fear." I

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