Very true
Projections are only as good as the underlying assumptions and the accuracy of their predictions of the economy. Assumptions are often flawed and the economy is constantly changing during various points of the business cycle, making any long term projections problematic at best.
I'd love to find a good source that summarized CBO projections from year to year. If memory serves, in the mid 1990s, they were projecting deficits for years to come. Only, they were wrong. They then projected surpluses for years to come. Only, the economy went into recession and 9/11, so they were wrong again.