There are few problems that distance people from language proficiency. That is why it takes decades for some people to achieve a dicent level. It is possible to handle a language at a very high level during several years only if you do not make the mistakes I describe here.
1. Lack of Motivation
One of the mistakes is a lack of motivation. It ussually looks like this: “Oh, well, I need to learn German, but I got to do my report for tommorow”, “I should cook a dinner for my children, no time for the homework”, “I should clean my room”. And language learning is set aside. I have heard a joke about session at university. This follows like this. A student’s apartment is perfectly clean when session time is approaching given that it is normally dirty. It comes from the people’s laziness. And if you are in one of the abovementioned situations or similar try to understand what is your ultimate goal. Is learning your language is just your temporary hobby? If it really matters for you, you will find time to learn something after a hard working day.
2. No Consistency
And yes! consistency matters. A goal without a plan is just a wish! To be honest I used to be a little inconsistent as I was a child. I used to learn like around 80 words per day and not to repeat them. I mean, I had a target, so in fact I had a plan. But the problem was that I did not repeat the words the day after. So I hardly could remember them. Consistency is when you have a good plan to follow and you do not skip your small homeworks.
3. No Help in the Beginning
Well, it is hardly possibble to learn a new language from scratch without a tutor. I know there are some examples of polyglots who have mastered a language but I also assume that you will talk and write with mistakes, unless working with a tutor. Tutors are there for you to correct your mistakes and also to keep you motivated.
4. Bad learning materials
You should get a couple of good books to learn from. If you have your tutor he or she will probably print the necessary materials for you. If not then read some forums, articles with recommendations of books for your level. Good grammar book is also essential because it sets the fundamentals. And it is a good investment in the future.
There are just few problems that came to my mind this evening. Probably you have some other things that stop you from mastering the language? Feel free to share it!