The “it” here can be almost any kind of organization – a person or an empire. It takes a long time for it to grow – but death can come suddenly – and is always final.
“So what?” You may say, “People have been saying this for thousands of years. Why bring up this depressing stuff now?”
Because in our time we need to be reminded of this again. And to notice where we are in the slow growth, sudden decline curve.
Not too long ago, Americans thought their economy could grow forever. And could not believe it when it leveled off – and then in many cases, dropped precipitately. What was going on?
Probably it was just the rise and fall of another civilization. The people near the end are always surprised when it happens.
Is this end inevitable? No, but it would take an unusual people to stop it. A people, or a civilization, usually develops skills to make them successful – but when they become successful, this changes their situation so much that their skills no longer are useful.
So far, no civilization has been able to see this – and to change fast enough to prevent its obsolescence.
Another people always arrive with new skills – but this is a slow process and can take thousands of years.