Tough Times
Although Invigoration allowed Lith to avoid sleeping, it wasn't without side effects. Back when he was still at home, he had several opportunities to relax, like when hunting for food, teaching Tista fake magic, or simply spending quality time with his family.
Now Lith was relentlessly working like a machine, piling up stress without any break outside his three daily meals. Over time, the accumulated mental fatigue made him more cranky, nervous and aggressive.
It was something the Professors would not notice. Lith treasured them, and did his best to hold his temper and treat them with the respect they deserved. The same applied to his 'friends'.
After his last heart to heart with Solus, he tried to spend more time them, to give her what she needed, more emotions and human interaction. It would soothe her depression and wear down his nerves, but he didn't care.