It depends on motivation: is my motivation to learn something new or play around for fun? Then I'll choose whatever I'm interested in learning. If the motivati

It depends on motivation: is my motivation to learn something new or play around for fun? Then I'll choose whatever I'm interested in learning. If the motivation is to build something I actually need independent of the stack - in other words, something I expect to be paid for building, or has some other utility - then I'll use what I know. That doesn't mean I won't learn new things, but I'll learn those things in order to get the job done, rather than for their own sake. That doesn't rule out small experiments - for example, trying out an individual library to accomplish a task - but the overall stack will be something I'm familiar with.