That's actually bad advise. Nothing worth learning will be finished learning before you run out of joy for it.
The best example from my experience is learning songs in a foreign language I'm studying. First you listen to a song you really enjoy and partly understand. Then you sit down and translate it. For most songs this will not just be tedious work, but also take out some of the joy of this song, because if you understand it you realize some of the text is outright stupid. That's normal.
Then you go and learn the song. That's not hollywood romantic stuff, with exciting background music and action heavy cutscenes. That is sitting down and repeating line 1 until you hate it. Then repeat it a few times more. Then do the same with line 2. Then do the same with the combination of lines 1 and 2. Then line 3. Then line 1+2+3. Then line 4. Then line 1+2+3+4, [...] then repeating line 1+2+3+4+5+6+7+8 but sadly by doing that you completely forgot line 2 and you always reorder line 5 according to your mother language's grammar instead of the one used in the lyrics.
In the end, you really hate the song. And you sing it quite badly if you just spend time learning the lyrics and no time on the melody and composition of the whole thing. When you can really sing it for other people to enjoy listening, even the slightest bit of magic for it will be gone for you.
And only after you done this multiple times and you start to have a collection of songs, ready to apply to different circumenstances, able to apply the feelings of the moment for a unique interpretation of your own, then you will find joy in it again.
And I can promise you, if you can get to that point it doesn't really matter anymore if in the beginning it was something you enjoyed or not. You made it your own, and that is what is much more enjoyable.