A lot of people see foreign language learning as a kind of black box. You start the process, take a course, and somehow then end up fluent on the other side. No one knows what happens in between... But this whole process can and should be demystified.
If you want to get in shape, you can be incredibly scientific about it. You can measure how many calories you take in, and how many you put out. You can map out the muscular system of the body and design a program that will work each component. You can balance your workouts between cardiovascular and strength-building. There are many different ways to get fit, but the fundamental principles remain largely the same.
In foreign language learning, there are muscle groups and exercise types. Just jogging will not get you fit. Just doing pull ups will not help you run faster. Languages are complex systems like the human body. We know that when approaching a new language there are certain elements that must be learnt in order to become fluent. Avoiding these elements — like avoiding particularly painful workouts — simply delays progress.
I know people who have been trying to get in shape for years and people who have been putzing along with a language for years. It takes less combined effort (and significantly less frustration) to simply bite the bullet and put yourself through some kind of intensive training program. What you need to do this is detailed knowledge of all aspects of the content that it is essential to learn and the processes for internalizing that content. It's no mean feat, but it can be done.
When you understand what content is necessary and the processes for mastering that content, then you can work with a clearly defined objective. Say you want to get from zero to a B2 level in the language in a certain time period — you can clearly map out what every minute of that time period needs to look like in order to attain your objective. That's very exciting, and gets rid of the "black box" attitude about language learning.