Scheduled maintenance is half a solution.
Planned and preventive maintenance is mostly reliant on scheduled checks but breakdowns still occur and in most cases there is no effective way to predict issues beforehand. However, spot checks offer limited peace of mind when an asset or environment needs to be running properly all the time.
Reactive maintenance isn't the other half
The result is that when problems occur there is a rush to meet SLAs and respond quickly and effectively. And when customers are experiencing problems there is significant pressure on engineers and administrators. Ideally, problems would be avoided because the signs of failure would be spotted early enough for action to be taken in a planned and effective manner.