When I'm tired and don't want to really work, I start procrastinating. The problem is that I'm not aware of it.
I hide it behind being productive. Doing something, anything that's now what I should be really doing at this point in time.
Some examples span from: Let's check out the MEAN stack and try doing something with it, let's check out Machine learning, AR, VR, Blockchain and everything in between. To something more productive like finishing an app for a client for which the deadline is months away instead of the one that is due in one week.
It doesn't only apply you when you're busy. Even if you have time you should really consider what's with and what's isn't. If you already know how to make a website using one stack, is it really worth to learn a completely different one for this new project? Sometimes it is, because you learn a different view on the topic, other times it is not because what you're doing is only procrastinating on the actual work you need to do.
If it's something you really want to learn go ahead, otherwise time would be better spent working using languages and tools you already use and know. Reading one tutorial without ever coming back is not really going to leave you much. You need to at least make one whole project from start to finish to truly learn a new language/framework/skill.