The golden rule in my experience is that you can have both, if being careful in the proportions. Usually I limit new things to 1-2 concepts/tools a time, and use well tried ones for others. This way I usually manage to get stuff done and avoid getting stuck in my comfort zone.

Note: I have some hobby projects with minimal progress, where I ignore the golden rule and try new stuff all the time :)

As a counterpoint, I recently built something in a framework (Rails) that was relatively new to me because the framework had large amounts of functionality available as open source components (info in profile).

I reviewed other options, including technologies that I was more familiar with, but the risk of slower development while I came up to speed was outweighed by the increase in speed to market.

But often, you only learn something by building something.

performa prototype build of a thing you've already built. You'll gain the new knowledge in context, making it even more valuable.

I did just that about a year ago. I moved over from a an MS stack to a Linux/Node/Postgres stack. And while I finally got the damn product shipped - it was a terrible idea to change my tooling/environment so dramatcially. Everything took way longer. And honestly, the quality of the end product is worse.

What motivated the change? Were Linux/Node/Postgres technologies you were familiar with in comparison to the MS stack you were using? This can be problematic regardless of the technologies involved.

This can definitely depend on the technology and the use case. For instance, I'm building a .NET desktop application and started using WinForms since I have several years experience with it. I scrapped that and started using XAML for the first time and I am already more productive in XAML than I am with Winforms. I have a cleaner UI and an easier time with the architecture due to the data binding.

My point is that there are technologies that if you are using a technology that is a pain in the ass (Winforms) but that is all you know moving to a newer technology that has been designed to be easier to use can not only benefit what you are building but even save you time in the long run.

Or you know, many set out to neither learn nor build, mostly to avoid chores and homework, and somehow end up having learnt and built and ended up with a good technology job.