Why is it hard to say what one means and mean what one says?

In saying what one means one is first hopefully thoughtfully thinking through what one should say and meaning what one says is in translating that thought into action. A lot of people draw their own conclusions to the words they hear coming from another but does assuming what one meant the responsibility of the talker? Should anyone who hears try and do some thinking for themselves about what was heard? or if they can't can't they ask for more clarification before taking it for a fact? Words are ideas and the implementation of them is left for who ever pleases and not necessarily the responsibility of who authored it only.