I've been studying French for a while and there is still so much I can learn. When I hear other people speaking it, it still takes large amounts of concentration to try and understand what they are saying.
For me, when writing, I can see what I'm writing, if the spelling is right, and it's easier to see what mistakes I'm making. It's also easier to fix the mistakes. When I'm speaking, I have to arrange it in my head fast and I'm a visual person so that can be hard for me.