CBO debt projections: Too optimistic or too pessimistic?

Every year, the Congressional Budget Office (CBO) makes projections of what the federal budget will look like, in particular, what the government debt and annual deficits will be. Note that these should not be seen as forecasts since CBO projections aim to measure what will happen over the next 10 years assuming no change to any laws (which is of course unrealistic). Nevertheless, Hanno Lustig examines the US federal debt and deficit relative to CBO projections.

Regarding debt to GDP ratios, CBO projected debts that were higher than actual from about 1985 to 2000. Since 2000, however, debt projections were actually much lower than expected.

The data on surpluses each year was relatively similar. Form 1985-2000, actual surpluses were higher than CBO projections. After 2000, however, actual government surpluses were much lower than CBO projects. The 2020 downward spike is of course the COVID stimulus funds, but even without that spike, the trend is fairly consistent.