I wonder if his family's financial situation might have something to do with his insomnia. I mean not buying new shoes because of money problems is a pretty common trope, at least in western media.
@NorwegianJap it's been explained that they don't have money problems but he doesn't want to ask his dad for money his insomnia is mostly due to his parents divorce.
I used to think like him too in my early university years when it was late at night about how much sleep I would get if I fell asleep right now. I completely fucked my day/night rhythm since then and have had to rely on medicine to get tired enough for a good sleep.
@NorwegianJap the reason is not financial I believe. Most likely those shoes are the last memento of his mother who left him. The divorce was pretty traumatic for a kid therefore his current insomnia and other issues.