What happens if requirements change? What happens if a related technology is invented which would make your current design more efficient? Do you class changes

What happens if requirements change? What happens if a related technology is invented which would make your current design more efficient? Do you class changes like that under maintenance? And how do you check your theoretically 'no-maintenance-required' design genuinely doesn't need any maintenance? And how do you get round the catch 22 that you can't build a perfect system without perfect knowledge about what to build, but you can't have perfect knowledge without feedback from an existing system? Instead of building a product that theoretically never needs maintenance, I'd rather build a product for which maintenance is easy.