[The Buddha said], "Sona, you were a musician and you used to play the lute. Tell me, Sona, did you produce good music when the lute string was well tuned, neither too tight nor too loose?"
"I was able to produce good music, Lord," replied Sona.
"What happened when the strings were too tightly wound up?"
"I could not produce any music, Lord," said Sona.
"What happened when the strings were too slack?"
"I could not produce any music at all, Lord," replied Sona
"Sona ... You have been straining too hard in your meditation. Do it in a relaxed way, but without being slack. Try it again and you will experience the good result."