It's pretty much just that simple, but let me add a corollary to the rule: if doing something is going to kill your motivation to learn a language, stop doing it. This gives you a free pass to ignore any language-learning suggestions (including, of course, my own) that would kill your motivation.
But if something is only going to damage your motivation and thus merely reduce the time you spend learning languages, you need to consider how much more efficient that thing is before giving it the old heave-ho.
Let's say you spend 10 hours per week on language learning using method A. Under method A, you learn on average 20 new items (vocab, grammar rules, pronunciations, characters, etc.) per hour spent. Your result is 200 new items per week.
Let's say method B offers a better return of 30 new items per hour. If you like method B, then switching to it is a no brainer and you end up with 300 new items per week.
But let's say you don't like method B, and using it hurts your motivation such that you end up spending 40% less time learning your target language. That means you end up only spending 6 hours per week, resulting in only 180 new items per week. While this still speeds up your per-hour progress, it slows down your long-term progress.
But that does not mean the rule is as simple as "if something causes me to spend less time learning, I shouldn't do it". Let's say that method C is the same as method B except that the improved return is boosted from 30 to 40 new items per hour. Even spending 40% less time than under method A, those 6 hours spent will result in 240 new items per week, increasing both your per-hour and long-term acquisition speed.
|Method||Items learned per hour||Reduction in time spent||Hours spent per week||Items learned per week|
Of course, it's easy to make a choice when you've got clear numbers laid out for you like this. In the real world, however, you're pretty much never going to have these kinds of numbers. This will mean you'll typically be forced to rely on guesstimates, but nevertheless you should always consider the efficiency of a language-learning suggestion together with its affect on your motivation and thus time spent.