"you mean that first you study patterns, and after learning them properly, and dancing long enough, it all just turns out into a one whole dance without giving thought to "now I'm dancing this pattern", right?"
Not exactly.
Let's take the molinete. You can start this sequence of steps anywhere, but it is basically, for the woman: take a forward step, collect, take a side step, collect, take a back step, collect.
Often when dancing with beginning through intermediate dancers, when they realize that they are taking a forward step, and the man is staying in place, and they are beginning to rotate around him, they launch into the pattern of steps for the molinete.
But, it is actually possible to lead each step in the sequence. There is a pretty specific rotation of the man's torso that should produce a back step, and a different rotation of the man's torso that should produce a forward step.
It is possible to lead two forward steps in a row, rather than a forward followed by a a side step. Or any other comination of steps. But, not only does the leader have to know how to do this, but the follower has to feel and understand what is being asked for.
You already know the pattern, but you do something diffferent to add richness to the dance.
Rather than it being "one whole dance", it's one step at a time through the whole dance with each step involving lead and follow.
I have had instructors who will teach a pattern, then immediately show us how to break the pattern.
Me, I guess I get bored easily, so this really appeals to me. Of course with Argentine Tango, the challenge was there, and was quite the challenge.
I now tell my partners, when they ask me if they did what I "wanted them to do", that what really matters is what they did. And that as long as they let me know where they are (a whole 'nuther subject involving posture, how they step, and keeping their weight towards me), it doesn't matter.
Now we're both improvising!