Japanese grammar

[The Summoner of Leviathan]

But if you don't know their functions you can't really use them. Also, if you use the wrong particle, it can change the whole meaning of a sentence or a nuance of meaning. So using them without knowing their purpose or role can complicate matters.

1. ロケットは宇宙で飛んでいる。ロケットは宇宙へ飛んでいる。
2. ロケットは宇宙を飛んでいる。

In the first sentence, you are implying that the rocket flew from the Earth to space. In 2., the rocket is flying through space.

By practising you get a better feel for the difference, but you first need to know what the difference is.

A more subtle example is:

1. カレーライスでいい。
2. カレーライスがいい。

The difference between the two rather subtle but important. The first implies that curry rice is sufficient like it is not necessarily the speaker's favourite but they'll make due. The second one implies that they like curry rice.

Personally, the more I practise は/が, the more I understand the differences between when to use which.

Also, conversing in a language is different than writing in a language. Look within the differences in how you write, especially formal essays, and how you talk. The case of Japanese, the distinction is greater in my opinion. Most university classes are geared towards a textual ability rather than conversation which tend to take a secondary place.

Oh and the confusion would still take place with particles when you are talking until you mastered them. There has to be a framework of the language, whether implicitly or explicitly present, in order for the it to flow easily. That framework as you get older becomes more explicit and a lot harder to acquire. It is not as simple as "going out and practising it". Whether you are practising it through conversation and/or by text books, there will always be a point where something is confusing or hard to grasp.

I think your point is more valid in an immersion context, however for most university students such a method is hardly available. The closest thing is to get a language exchange partner (which I really should do!).

EDIT: I realize I being argumentative and opinionated. ^__^;;;