There's nothing wrong with doing stupid shit once. But it becomes habit quickly without constant vigilance. See Periodic's response in this thread.

I think that word 'learn' may mean 2 entirely different thing, and that's why the op may be confusing for some people. We can think of learning as improving your skills in one area, or we can think of it as exploring possibilities. For example you could learn some programming language (as your first) like C++ and then stop doing stupid shit and become expert at it, or you could do stupid shit like ingesting news about every new shine technology that comes out and settle for something else later, like ror. Succesful learning is for me a bit about balancing between 'breadth search' and 'depth search'.

However this is not exactly what the OP is about - I think author's point is to cut off things that doesn't work, and stick to those who do; it's about optimizing your learning methodology.

Also you can do really stupid shit, like browsing reddit all day long (which was my first thought when I looked at the title), but that's different thing, and it's quite obvious that it won't lead you to success.

First, don't be afraid to fail and make stupid mistakes. Then, after you've made those mistakes, examine them and eliminate them. I think the author is talking about the latter part, and that often this process of removing mistakes is all it takes to be good at something. This idea could be reassuring to you if you tend to think that you need a certain genius that you do not have in order to excel. All you need is the ability to recognize your mistakes and the will to get past them.