[xnickb]

Confidently wrong. Life is a bit more nuanced than that.

Look at any popular open source project and tell me not a single contributor was having fun while writing it.

I can give you examples of very high quality open source projects where I know for a fact that the person/team behind them were just having fun.

[ankurdhama]

Let me clarify what I mean by for fun vs professionally. For fun means you make decisions based on "That feature would be fun to implement". Professionally means you make decision based on "That's what good for business". Based on these definitions most of the open source projects don't fall under "professionally" category.

[9rx]

Aside from maybe a handful of projects that got lucky squatting on the right name (e.g. left-pad), are there any popular open source projects that have become popular on "that would be fun to implement" rather than "that's what is good for business" (understanding the user, answering issues, implementing requested features, etc.)? The chances of your fun overlapping the exact market need seems rather slim.

Even among unpopular open source projects, I expect most of them are published as a way to demonstrate ability to employers rather than "that would be fun". The latter projects do exist, but it is surprising if they make up most open source projects.