Wu Long initially thought, that he would be able to obtain the Fire Rune relatively fast, even faster than the Wood Rune.
Not only did he understand the fire attribute far more due to studying Alchemy Dao, but he also already had Lightning, the power commonly called the Heavenly Fire.
But all of his attempts at comprehending, and thus obtaining the Fire Rune up to now, ended in failure.
And only now, he understood why - he was missing a step, or simply overlooking it.
He tried to obtain the Fire Rune, without first possessing the Heat Rune.
This was the reason he was so dumbfounded after recognizing the Heat Rune, which turned out to be already in his possession, ever since he obtained the Sound Rune.
After accidentally producing heat with vibration, and then comparing it to heat generated by Lightning, it caused him to more closely examine how the Lightning actually produces heat, and compare it with the heat he obtained with vibration.
