Life and Death.
Now that Ryu thought about it, he rarely tried to comprehend things that were too complex. It could be said that his Dao and Spacetime were his two most complicated paths, but one existed as a focused attempt to make comprehending other things much easier, and the latter came to him naturally courtesy of the mysterious Zu Ancestor Visualization.
When Ryu took a step back and realized this, he found it all to be a bit amusing. He had all this talent in comprehension, yet he usually spent it on the easiest concepts to understand.
All things considered, Fire and Lightning were just elements, and they were among the easiest paths to comprehend. His Weapon God Auras were also relatively straightforward. The paths were already carved out by others, and there were also so many to observe, so how could it not be easier? In fact, the only times he had tried to deviate from those paths, he had ended up having to abandon it not just once, but twice over.