I won't sugarcoat it: Leading cruise line operator Carnival Corporation (CCL -1.95%) has been a poor long-term investment.

Over the past 20 years, Carnival's share price has taken investors on a bit of a roller-coaster ride but overall is about 64% lower. However, because it has paid dividends in the past, Carnival's 20-year total return has been a somewhat less terrible negative-45%.

This means that if you invested $1,000 in Carnival stock 20 years ago, in March 2005, and reinvested any dividends you received along the way, your investment would be worth about $550 today.

Why has Carnival performed so poorly?

The short explanation for the terrible performance is that Carnival's business was deeply affected by the COVID-19 pandemic. Cruise lines were essentially shut down when the pandemic started, and they didn't start sailing at full capacity for at least a couple of years after the initial shutdowns.

In fact, if you had invested $1,000 in Carnival in 2005, your investment would have been worth as much as $1,835 in the pre-pandemic years.

Two statistics show just how damaging the COVID-19 pandemic was to Carnival:

• The company was forced to issue lots of new stock, thereby diluting shareholders, and Carnival's outstanding share count is 90% higher than it was at the beginning of 2020.
• Carnival was forced to take on more debt to sustain its operations. Carnival entered 2020 with about $12 billion in long-term debt, but that ballooned to $33 billion by the beginning of 2022.

To be fair, Carnival has made progress in recent years. Demand has certainly come roaring back since the pandemic ended. Carnival's revenue is actually higher than it ever has been, and the company's debt has declined by billions from the peak. But the damage the pandemic did to Carnival's business was immense.