It's difficult to do things in a proactive way

As things get older, it becomes more & more difficult to identify what is the root cause of the problem whenever there is a problem. The problem could happen at any point or multiple points down to the whole path. You have to isolate them from each other and fix them one by one. Sometimes it's just not possible to figure out the root cause. You don't know which is caused by which since they are all correlated. It's pretty much like us, human-beings. It may take several days or even several weeks to fix all the issues and get the problematic system back to normal. The system availability drops a lot during this period, of course. So proactive is always much better than reactive. Sounds like everybody knows this.

However, in a real world, usually it's hard to actively replace things until it has a problem. People would say "why do we need to replace it as there is no problem at all? look, it's running well!". Or sometimes they would say "I understand your concern. But you know, we currently have a tight budget. It's hard to get approved if we raise the request. After all, things are still running well. Let's play by ear!" But, when a serious problem happens and the system becomes unavailable, these guys just get nervous. "You must fix it ASAP! You must bring the system back by today! I don't care how you do it, you gotta get this done!" Sounds pretty similar? This happens in our life almost every day.