I think there will always be an element of surprise with watercolours. Totally understand what you mean by mastering the art of the flawless though randomised processes.

I also learnt recently that in 'art therapy' for people with autism, crayons and more 'soft' media, like watercolours, are given to those who feel a need to control their environment. And as they make progress, they're slowly allowed to use pencils and pens.

In any case, pen or watercolours, it's interesting to see how you use both. Big fan, if that's not obvious already!