If you understand how credit scores work, you'd realize that what you've experienced doesn't contradict the parent's claim. Specifically, having low credit utilization (ie. low credit used compared to available credit) and high diversity of accounts is beneficial for your credit score. Closing accounts is bad for both of these, hence why your credit score dropped. It doesn't invalidate the parent's claim that you can have good credit by just using credit and paying it back on time. FWIW I have a few credit cards that I pay on time every month, and my credit score is pretty good.