Deciding between a tech that you already know and know will work well for the problem, and a tech you don't know - that's an easy choice. A harder choice is wh

Deciding between a tech that you already know and know will work well for the problem, and a tech you don't know - that's an easy choice. A harder choice is when you know the tech you known doesn't quite fit. Do you go with what you know, or do you try something new? Concrete example I'm currently considering: If I want to make a web pages that does some background work, should I use Django and Celery like last time, and spend months tweaking Celery settings I don't understand and still feel like the system's kinda clunky (like last time). Or do I use Elixir where there's little difference between handling a HTTP request and running a background task, and where I can just spin up a few thousand threads to monitor background tasks? TLDR: What do you do when "what you know best" isn't the right choice?