I answered this question on the italki forum, but let's face it, serious language discussions are pretty rare over there. So here is my answer - feel free to give your own opinion or comment on mine. "I assume you mean conversation when you say "speak". There can be many reasons; I think it depends on the individual. If you often write, but rarely converse, for example. Or it might not even be true. When I first started writing Russian, I had already been conversing for 2 years, so writing was harder than conversing at that point. But for people who have been doing both for a long time, I think it's often true because you have time to process your thoughts, use a dictionary, grammar, etc, when you write. You don't have this luxury when you converse, which can lead to more mistakes."