Complex sentence: Despite his intellect, he regularly displays a lack of common sense, and has a superiority complex, but also possesses childlike qualities, of which he normally seems unaware, such as extreme stubbornness.
Split into simpler sentences: Despite his intellect, he regularly displays a lack of common sense. He has a superiority complex, but also possesses childlike qualities, of which he normally seems unaware, such as extreme stubbornness.