What is the "substantial evidence" rule?

"'The gist of the "substantial evidence" rule is: [] "When a trial court's factual determination is attacked on the ground that there is no substantial evidence to sustain it, the power of an appellate court begins and ends with the determination as to whether, on the entire record, there is substantial evidence, contradicted or uncontradicted, which will support the determination . . . ." [Citations.] [] 'So long as there is "substantial evidence," the appellate court must affirm . . . even if the reviewing justices personally would have ruled differently had they presided over the proceedings below, and even if other substantial evidence would have supported a different result. Stated another way, when there is substantial evidence in support of the trial court's decision, the reviewing court has no power to substitute its deductions.'" (Rupf v. Yan (2000) 85 Cal.App.4th 411, 429-430, fn. 5.)