Ryu's veins bulged across his forehead, but his demeanor was calm and unhurried. He was confident, and his mind was more than strong enough now to manage it all. In terms of comprehension, for him, the Heaven and Earth characters were the easiest, because they were the true core of his Dao. However, logistically, they required the most qi and demanded the most of his control.
While he was condensing the Earth Character, he realized that if he followed through with it alone, forming the Heaven Character afterward would be impossible. It was akin to trying to insert a new rope into an already completed and complex knot. It wasn't possible to bind them perfectly unless the first knot was undone, but if the analogy was taken to reality, undoing the knot would mean destroying his already created Cosmic Seeds. That was unacceptable.