Just to add to Munro's answer with a couple of other examples that might help. Note that "get you so far" or "take you so far" are often used as a lead in to a statement as well. - You're charismatic personality will only get you so far (you can't just rely on being liked. It implies that you're not doing something else that you should, like working hard, for example) - Reading about how to learn English will only get/take you so far. You need to use it too. - Being clever will only get you so far. At some point you're going to have to study as well.

you are right, the phrase “only so far” means that it has its limits. the phrase is usually used in a vague way like this, where it is unclear what that limit might be.