Amazon turns 25 on Friday, which serves as a reminder that CEO Jeff Bezos has repeatedly talked about his company's inevitable demise.

Bezos has said that the life-span of big companies is "30-plus years," meaning Amazon could have as little as five years left in the tank.

Such chatter is strikingly unusual for a CEO of a major company, but it seems a fear of failure, and talking about that fear of failure, propels Bezos on.

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Jeff Bezos founded Amazon on July 5, 1994. Some 25 years on, it has grown into a tech behemoth — momentarily the most valuable company in the world last year — and made him the richest man in modern history.

But the billionaire seems convinced that Amazon is doomed to die. Three times over the past six years Bezos has talked about the firm's inevitable demise.

Such chatter is strikingly unusual for a CEO of a major company. Media trained within an inch of their life and with demanding investors looking over their shoulders, senior executives are normally unflinchingly positive about their firm's prospects.

But it seems a fear of failure, and talking about that fear of failure, propels Bezos on. Here are some of the times he has talked about Amazon's inevitable demise:

2013: Bezos says big companies only live for a "few decades"

Bezos spoke to CBS show "60 Minutes" in 2013 to show off Amazon's burgeoning automated drone delivery service. "Companies have short lifespans... and Amazon will be disrupted one day," he said.

Read more: Jeff Bezos was wrong when he predicted Amazon will be making drone deliveries by 2018

Asked whether that fact worried him, Bezos replied: "I don't worry about it because I know it's inevitable. Companies come and go, and the companies that are the shiniest and most important of any era — you wait a few decades and they're gone."

Bezos added that he would love for Amazon's final breath to come after he himself dies.

2017: Bezos ponders an "excruciating, painful decline" in a letter to shareholders

Bezos elaborated on his "Day One" philosophy in a 2017 letter to shareholders, in which he answered a question he'd got in an all-hands meeting about what "Day Two" looks like.

"Day Two is stasis. Followed by irrelevance. Followed by excruciating, painful decline. Followed by death. And that is why it is always Day One," Bezos answered.

"An established company might harvest Day 2 for decades, but the final result would still come," he added. He then talked about how a company can "fend off" Day Two.

2018: "I predict one day Amazon will fail," he tells staff

In a recording of an all-hands meeting obtained by CNBC, Bezos was still just as convinced of Amazon's inescapable mortality.

"Amazon is not too big to fail ... In fact, I predict one day Amazon will fail," Bezos said in reply to a staffer who asked about big businesses like Sears going bankrupt.

"Amazon will go bankrupt. If you look at large companies, their lifespans tend to be 30-plus years, not a hundred-plus years," he said.

Bezos went on to say that it was his job to delay that date by as long as possible. Amazon turned 25 years old today, so it is fast approaching Bezos's 30-year benchmark.

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