Actually, Yu Sheng understood very clearly—he was not some kind of "professional."
Of course, if you must count the business license, then he was indeed a licensed "Spirit Realm detective," which made him a professional among ordinary people when it came to confronting supernatural phenomena. However, in such a highly specialized situation as this, he was self-aware enough to know his limitations.
Encountering a stranger from the Exotic Realm and using his fearlessness to map it out, or facing an unknown entity to test its strength—even if he were to be thrown at an undefeatable Dark Angel—even in such situations, he'd have no problem. But this tower before him looked like a cultist's high-level stronghold filled with secrets. Going in to investigate as an ignorant novice could create chaos, and while he might not uncover anything useful, he would almost certainly meet his end inside.
