Finances in order and have the willpower not to spend money you don't have, just because you can. Some people lack that, and it's smarter for them to just avoid the constant temptation by now having a credit card.
When people say to use a credit card to buy everything they typically mean using it in pace of your debit card: only spending money you actually have right now and could pay off instantly and never carrying a balance. You're in it to rake in fraud protection, rewards, and a higher credit score for if/when you want to buy a house or car.
You don't even think about the idea that there's a line of credit attached to the card that extends longer than 30 days.
Chase lets you configure the payments to pay in full every month. I was very surprised to see this, as the bank ideally wants you to pay the minimum and interest.
Also one thing people often forget if carrying a balance - if you have balances with two different interest rates (say cash advances or balance transfers first vs. purchases or if the card issuer has raised the interest rate for purchases after a certain date) they would like you to think that "any payment above the minimum goes towards the highest interest balance" means that the whole of the given payment goes towards said balance. In point of fact, only the amount of the payment above the minimum does, the rest goes to the lower interest balance. This can sneak up on people who don't actually read their statements and destroy any form of credit progress.
You don't even think about the idea that there's a line of credit attached to the card that extends longer than 30 days.