What does 弹性 refer to in this sentence?
《汉语大词典》


  2.比喻事物的可多可少、可大可小等伸缩性。


《懒虫简明汉英词典》


  flexibility


人的心理因素(的)弹性很大
The flexibility of human's psychological factors is great.

If a doctor tells a healthy man that he has cancer, he will get sick very soon.
If a woman has cancer, and the doctor tells her that she is healthy, she can live longer and healthier.

This is the psychological effect.

人的心理因素弹性很大 also talks about this effect.

All coaches encourage the athletes before the competitions because an athlete may be confident or without confidence.

The 弹性 here refers to this range, active or passive.