At present, Zhou Tian seems to have the upper hand, but given the situation at that time, the possibility of him gaining much advantage in future battles with the Space God King is actually quite limited. On the contrary, the small gain Zhou Tian enjoys now is solely due to his own powerful strength. So, if things change in the future, and Zhou Tian is either trapped or the Space God King's strength surpasses his own, Zhou Tian might as well stop thinking about how to kill the Space God King. Instead, he should think about how to ensure his own safety at that time.
Being in such a position at that time, Zhou Tian's mood could not possibly be anywhere pleasant. Hence, in light of the circumstances back then, realizing that being stuck outside the Divine Realm for a while had completely ruined his originally excellent situation, Zhou Tian's mood became exceptionally bad.
