A determined professional will strive to keep learning throughout their career. Sometimes that learning is easier. Sometimes it’s harder.

If you focus on facts, you’ll find learning gets easier. The act of learning makes you a better learner, and you can build on previous knowledge. Learning your fifth programming language standard library is going to be easier than learning your first programming language’s standard library.

Deeper hard skills are sometimes easier and sometimes harder. They can be easier when they’re just reformulations of stuff you already knew. They’re harder when they represent new paradigms unlike anything in your experience and thus contradict the intuition you’ve developed over the years. This can also challenge your ego, making you stay within your comfort zone of expertise so you never feel like a n00b.

What will keep getting harder to learn are the soft skills. One reason for that is that that type of learning often comes from mistakes, and as you become more established and more comfortable, you may make fewer mistakes. It’s easy to see that as a positive development. It mostly is, but if you’re not making mistakes, you’re not challenging yourself, and you won’t be growing.

But I think the biggest challenge is that, inevitably, what’s left for you to learn is what’s hardest for you to learn. Maybe there’s a problem or an ability that’s invisible to you, that you can’t even perceive, like color-blindness. Maybe you can see it, but you don’t understand how it happens. Or, perhaps you can see the problem and understand why it happens, but you struggle to exercise the self-control or skill to deal with it. The problems that you can readily see, understand, and deal with? You took care of those when you were 25, when you were 30. Once you get a decade or two into your career, those low-hanging fruit have been plucked, and all that’s left are the ones that are hard to reach (or in a different tree entirely).

What’s particularly galling is that the things you have to learn are yours to learn. Some things come easily to you and only with difficulty to others, perhaps never. The opposite is true as well. I have no idea what makes some things easy for some people but hard for others, but I do know it can be surprising what people have trouble understanding. I’m sure what I’ve failed to understand has been surprising for others.

I think this is one reason (of many) why many people’s careers stall out at a middle level. The way that you’ve been learning and improving stops working. The problem is nobody tells you it’s stopped working. You just… stopped, and unless you find a new way of identifying your blindspots, understanding what’s in them, and adapting your behavior, you’re going to stay stopped.