Programs, like people, get old. We can’t prevent ageing, but we can understand its causes, limit its effects and reverse some of the damage.
If McDonald's were run like a software company, one out of every hundred Big Macs would give you food poisoning, and the response would be, "We're sorry, here is a coupon for two more."
The secret to building large apps is never build large apps. Break your applications into small pieces. Then, assemble those testable, bite-sized pieces into your big application.
We build systems like the Wright brothers built airplanes — build the whole thing, push it off the cliff, let it crash, and start over again.
Most software today is very much like an Egyptian pyramid with millions of bricks piled on top of each other, with no structural integrity, but just done by brute force and thousands of slaves.