At least for me, only watching something done step by step does not guarantee a full grasp - or least I am not sure beyond any doubt that I understand, until I try myself. If I watch a tutorial, I am doing the same thing alongside it. This of course varies with the complexity of the task. How to put together a 3d printer? Yeah watching a video of it done will give my a full grasp of what I need to do without practicing. How to implement a support vector machine while understanding the underlying math? It's not sufficient to see it done.

Similarly seeing something written out is not the same as writing it (in terms of the processing going on in our brain)