Yoga Sutra 2.43
Kayedria Siddhir Asuddhi Ksayah Tapasah.
When you practice yoga sensory perception awakens more.
Tapas means to burn or create heat. It can also mean accepting but not causing suffering (ahimsa) in order to purify the body and mind. Tapas is the ultimate self-discipline, which is the power to control the body and it's senses. If we accept everything (finding the benefit even in painful situations or circumstances) or even happiness (which is temporary also), what can affect us?
"Tapas is necessary. "No" is easier in the moment. Going to the unknown is the challenge." --Anand