We put systems in place for a lot of things. 

Companies do it for hiring, for promotions, for making launch decisions, etc. Families do it for deciding where to go out or where to go on vacation, how to manage their bills, how to do their chores, etc. And individuals do it for deciding what they want to spend their time on, what improvements they want to see in themselves, etc.

The reason we do it is so that we don't have to repeat the decision making each time and thus arrive at more consistent results each time. We also do it to ensure that these things run on their own, like a ball pushed down a hill, thus freeing up our time to focus on other things. 

And a good system does precisely that. It frees up our time from making some decisions so that we can spend that on making other, potentially more important, decisions.

If we are having to intervene and make exceptions too often, then the system needs to be replaced. 

Another way to look at it is, how often do you stick to your principles or behaviours that you want to see in yourself? (Like waking up at 6 everyday, or not eating junk food, etc)

If you're having to make exceptions too often, the principle (which is just another system for decision making) is broken and you need a new one.