No roof is meant to last forever, and even the best of them lose their structural integrity over time. If you own a very old home with a once sturdy terracotta or slate roof, you might expect it to last forever, when the roof might be on its last few breaths before it gives up the ghost.
This is already a good hint to know when your roof is too worn out, since you can tell based on how old it is. If you have all the documents attesting of the roof’s accurate age, or if you remember when it was installed, it’s easy to tell whether or not it has to be replaced based on the type of material used in its construction. On that note, you can already know that an asphalt shingle roof shouldn’t last much longer than 20-25 years even under the best conditions, while protective metal roofing in Pensacola should be expected to last for more than half a century.
If you notice that any repairs you make just end up being undermined by new damage, it may be that the roof is too old and worn out, or that it’s just badly installed. In both cases, you can consider it worn out and incapable of protecting your home, so a replacement is definitely in order.