Author here. I considered including this but didn't want to ramble on longer than I already had. Plus, the story isn't really that interesting. Unlike what some commenters below suggested might be possible, I don't have a French-speaking significant other.

I started learning very casually sometime in November using the Duolingo mobile app. After a while I switched to the desktop version of Duolingo and felt myself making pretty good progress. I enjoyed learning French enough to keep at it, and after a couple months I got the idea to move to France after finishing up my master's program. That probably won't be the case anymore, but for most of 2019 I had the motivation to become fluent enough to do pretty well in case I ended up moving to France.

I don't have any French speakers among my non-acquaintance friends, and absolutely 0 French-speaking family. So, there has never been anyone in "real-life" for which I was motivated to learn French. However, wanting to move to a foreign country was definitely enough to motivate me for the better part of a year.

I feel like the number one motivating reason is having a significant other who has a different native language. This also makes it a lot easier to make progress because you basically have your own tutor who is also motivated to patiently listen to your struggles.

There's a Spanish saying that goes something like: the best way to learn a language is in the bed or the crib.

Nothing is quite as motivating to learn a language than dating someone (or, more likely, trying to) who doesn't speak English very well or is willing to refuse to speak it.

Learning a second language is a goal for many people.

It’s pretty cool to learn a second language and travel. I learned Spanish and backpacked from Guatemala to Buenos Aires over 9 months. I spent the first 3 months learning Spanish in Guatemala.