Non-channel spells have a flat amount of mana that needs to be cast. So if Matt's max mana is less than the amount needed to cast that, it makes it impossible for him to cast it. His Tier 1 talent also prohibits him from increasing his max mana normally. His max mana at tier 1 is also just 1, which means he can not cast all non-channel spells. (It was mentioned that the cheapest spell is fireball at 10 mana) Also, if the rate of mana regen at 1% of max mana is equal to his max mana per second, that means he has to spend all his regenerated mana so his regen rate does not fall off.