Answer:
the rebound effect; thought suppression
Step-by-step explanation:
The rebound effect: Also known as the rebound phenomenon.
It is defined as the occurrence or re-occurrence of symptoms that were either controlled or absent while being on medication, yet appears again when that particular medication is reduced, or discontinued in dosage.
Suppression In psychology is defined as the act of resisting oneself from feeling or thinking something. It is considered ineffective because even if a person suppresses his or her emotions, such as anger, the same feeling returns with a retaliation. And, this is what is known as the rebound effect.
The same is happening in the case of Cynthia, even if her teacher asks her not to think about the purple unicorns, she couldn't stop herself thinking for the same.