I actually disagree with this. Every time I experiment, even if it's a godawful failure, I've learned a lot of actual, usable things. And then, months later when I'm rummaging in my bag of tricks for a specific effect, I'll have a bunch of things to call on and an informed choice as to what works best. I did a whole bunch of experimentations with fire effects a while back, found one I liked, and I can just come back to it whenever I need to. It's a permanent upgrade to my visual arsenal.
And it's not like experimentation takes up my entire draw practise time. I typically do an entire picture 'standard' except for a few colouring and shading techniques that I take huge gambles on, even if it risks ruining the entire picture. I learned from Day 254, for instance, a lot about the limits and variance of the bristle brush, and I learned a three-point shading technique that I absolutely adore. In subsequent pictures I'll practise those lessons while experimenting with other things. In the same picture, I used lessons on solid black+transparency slider from previous experiments to get the shadow right. It all adds up, and flows together. Everything has use, like a big pile of Lego blocks.
Yes, attempting rote-drawing of standard humaniform heads until I can do it reflexively is an enormously appealing concept which often features prominently on my to-do list. But I don't have enough Lego to start building and refining the style I want yet. I don't have a good way to do hair. I haven't practised enough with skin tones. I can't draw figures in physical contact right. I want to experiment with these things until I've got understanding of each conceptual element, until my Lego box is full of pieces, before I work on refining a style.
I'm getting closer, but I'm also getting better at seeing which areas I'm completely clueless on.
Ouch, sucks mate.Aaaaand the best thing I've coloured in ages, yet I managed to only save it as a .png and not a sai file so I can't ever finish it, which really, really annoys me. And it also made me stop doing art for around two weeks...