is that not everything works as it did, or should!
And it’s not only the brain which can become unscrewed.
Other parts get used up, some parts can be replaced, others repaired. but they never work as well as they did.
Hearing aids, dentures and eyeglasses are part of the norm after a certain age.
Spare parts become available at great human cost, the death of one can mean life for another.
One day no doubt there will be miracle fixes but please pass me by so I can get on with my next lifetime.