Lento was living his life up until now with barely enough income to keep going, despite working long and dangerous days. So, he began to place too much value on money. He's not being sickly greedy for money, like Apple, but rather the concern over being able to make ends meet is haunting his thoughts. Even though he's now making good money. He was earning big with the corpse of the tarasque, for example. It would be beneficial for him to get rid of that mindset. But, like I said, it's not so bad either because he's not actually greedy.