That $25 t-shirt isn't $25 if you throw it on a credit card and let it rack up interest. By in large, understanding how interest works in the first place is just another problem with debt.
If you're constantly paying your debts, chances are what you're not doing is investing for your future.
Debt never seems to be a serious matter until you go to buy a home and you can't get approved for the lending.
The biggest problem with debt is that thinking about it is just stressful. Not having a plan of action can make debt seem overwhelming, thus causing financial stress.
Debt can be problematic on your mental health, but also your relationships! If you're in a serious relationship or married, debt can be a subject of controversy in your relationship!