''Don't take everything so literally!''

I've been hearing this for the last two or even three years.
Schoolmates ask me to not take everything so seriously and especially not so literally.
But what does literally mean? You rely on what's said, on the words which someone chose to express himself. How am I supposed to understand people when everything what they say is not meant literally but superficially.
Words do play a big role in our life: promises are words, speeches by politicians are words, confessions are words, etc.
So, we believe what people say and expect certain actions then. And if people's words contradict their actions then they are schizophrenic.
Back to the subject. My main problem is that I don’t understand how I’m supposed to believe people if they don’t mean everything they say. And the bigger problem is: I’m expecting people to think before they say something and because of that I always start to interpret and analyze what’s been said. This often leads to loads of misunderstandings because it usually turns out that the person who said something just said without thinking about it much. So, you don’t think before you talk  --> what you say can’t be taken seriously.
Now here comes my biggest problem: I haven’t met a single person (at my age) who’s like me regarding this subject. Even the ones who are pretty mature and smart also give comments and I keep wondering: Why did they say that? What were they thinking?
It always ends up with the same conclusion: They didn’t think at all!
And this can be quite exhausting for someone who’s always expecting people to talk sense. I guess my problem is that I sometimes think too much, trying to find the right words to express what I want to say in a way that excludes any misunderstanding. If you asked me about something I said two years ago I would still be able to give an explanation.. even if it was wrong I’d be able to explain the error in reasoning.
Of course there are certain situations in which one can overreact and you don’t take what he said personally because he was out of his mind but these situations shouldn’t become the standard.
Another crazy thing would be: I still remember certain incidents which happened 3, 6 or 9 years ago when I acted on impulse and had to bear the consequences later. To sum it up: I’m expecting too much from the people around me. Especially when I believe that there’s a hidden message or some sense in everything what’s said (do).
Can’t say that I’m willing to change that because as I said, words do play a big role in our life and if one just abstracts all the meanings of each and every word they’d get quite superfluous and meaningless. So, why still talking?