Run a non-commercial side project (Maybe open source)

A big part of learning is making mistakes and learning from them. As you grow in seniority, mistakes become more expensive in money and or stress. Trying new things on stable products in big companies is hard. So how do we keep learning? How do we get updated? How do we try new stuff to be seniors on it five years from now? Run a side non-commercial project.

Why no commercial? I will get deeper into this soon, but if people are paying for it, downtime, bugs, and instability are not quite acceptable. While learning, you probably have all of those, sometimes multiple of them, at the same time.