Whenever a system of structure is presented, it seems the first thing many of us do is put that structure in the "rules" category of our brain. It's a safe place to put things, but not always the appropriate story to tell ourselves.
An example that comes to mind is learning a line dance. (I'm talking regular people, not professional dancers!) There is a sequence of steps to follow so that a group of people can all do the same movements at the same time to the same music. It's a unifying and fun thing for a group of people to do the same thing at once. But do they all look the same or feel it the same way? Some put a little more wiggle in their hip, some do a little shoulder shimmy, some do a kick high, some barely do a kick, some stomp hard, others tap lightly. The structure and sequence of the dance provides a way for them to connect and experience the music and the dance. But the experience, even when done in a group, is a very personal one.
Creating a Zentangle tile begins with a structure, and the tangles have sequential steps that make them easy to learn. Just like a line dance (and yes, our tangle lines do dance!), learning the steps is just the doorway to enjoying the dance and the music in your own special way. How you shimmy or don't shimmy is your own relationship with the dance. And if, in the middle of the song, you decide to step out of the line and whirl around the room, then thank the steps (tools) that let you do that!
If we can challenge our "rule story", we might find that all along, the rules were just tools.