What is one reason that the constitutional convention decided they needed a document to replace the articles of confederation

Because the articles outlined an outdated tax system that would pay debts.

Explanation:

The initial Articles of Confederation did not have a systematic or right to collect taxes all across the states. Nor can the government regulate the interstate or international commerce. Rather, the Article gave the respective states the right and power to collect taxes and make their own laws, managing their affairs without the involvement of the federal government. But as the Articles of the Constitution were outdated and did not have a proper tax system that would enable the people to pay their taxes, the Constitutional Convention decided to draft a document that will replace the current outdated system.

teenagers are certainly stereotyped as moody.

most people view teenagers as naturally moody and grumpy, even when this is wrong. many teens are suffering from depression but it is brushed off as "just a phase" or "that's just cause they're a teenager"