A therapist treats anxiety using weekly sessions involving m…

A therapist treats anxiety using weekly sessions involving meditation instruction, breathing exercises, cognitive restructuring, and lifestyle counseling. After eight sessions, 15 of 20 clients report reduced anxiety. The therapist publishes these results as evidence that their unique combination approach is effective. What is the most fundamental limitation of this evidence?

A patient with migraines tries eliminating caffeine, gluten,…

A patient with migraines tries eliminating caffeine, gluten, and dairy from their diet simultaneously. After three weeks, migraine frequency drops from 12 per month to 3 per month. They conclude all three eliminations were necessary and refuse to reintroduce any. A nutritionist suggests testing foods individually. The patient refuses, saying “Why risk triggering migraines when I know this combination works?” What does this reasoning prevent the patient from learning?