Tomasz Cichociński:

It’s completely fine to deepen one technology or one programming language knowledge. It’s totally fine to just have a 9-5 job that pays the bills. But if you aim to level up, I’m highly recommending trying something new to broaden your perspective.

If you’re writing JavaScript, try some functional language like Elixir or ReScript. If you’re already familiar with high level, garbage collected languages, try something low level like Rust or even C/C++. Play with different concurrency model like coroutines or actor model.

You don’t need to change your job, you don’t need to ship products with it. Try to create something fun. You’ll thank yourself later.