The most common chart-of-accounts problems are too many accounts, duplicate accounts, and accounts filed under the wrong type. Each one quietly distorts the reports until the numbers stop being trustworthy, and each is easy to accumulate without noticing.
Over-segmentation is the usual culprit: a separate account for every small vendor or category turns a readable report into a wall of tiny lines. Duplicates creep in when a bank feed or an import creates a new account that already exists under a slightly different name, so a single real balance gets split in two. Wrong-type accounts are the most damaging — an expense recorded as an asset never reaches the profit-and-loss, so income looks overstated, while an asset recorded as an expense understates what the business owns. Two more habits compound these: leaning on catch-all accounts like Uncategorized Expense or Ask My Accountant as a permanent home instead of a temporary holding pen, and trying to delete accounts that carry history rather than inactivating them. None of these throws an error — the file keeps working, the reports just stop being true.