When I was in middle school, i had quite an....interesting teacher who one day taught us why we do not make assumptions. It had to do with dividing the word "assume" into three parts. In an effort to rise above crude, rude, and base attempts at humor, or to not talk about Shakespearean and Biblical donkeys, I won't tell you what he said, but I will talk about why assumptions are bad.
Wouldn't the world of Shakespeare, and our world for that matter, just be a better, happier place without assumptions. Maybe if we just were honest one with another. Lets take Hamlet for example. Instead of assuming your Uncle is evil, and hence playing crazy to find out, wouldn't it be infinitely more easy just to confront your Uncle about his murderous and incestuous habits, perhaps in an intervention of sorts. Lets look at Othello, assuming Desdemona is unfaithful, and grasping hold of that thought so tightly that even a kiss of pure innoccence almost persuading "Justice to break her sword" won't convince him otherwise and he ends up killing an innocent woman (Darn you Iago, you twisted sick man...). Romeo assumes Juliet really is dead and so dramatically takes poison and kills himself. A Winters Tale, Leontes assumes his wife too is unfaithful. Of course, he doesn't confront anyone, no, that would be too logical. Instead the best thing to do is to try and kill your childhood friend and set in motion events that will haunt you for 16 years. Much Ado About Nothing, Claudio assumes the worst in Beatrice causing many people much heartache and distress.
Good gracious people! Can't we just be open and honest with each other, hold off a little on the emotion and talk civilized before you stab your wife, or yourself? Sure, honesty sometime hurts to hear, but so does weeks of the cold shoulder and then getting stabbed to death, or turning into a statue for 16 years. I would rather have someone be honest than polite, in fact, it's impolite to lie or tell half-truths. Shakespeare teaches us well, that the world would be a better place if the inhabitants would work on their communication skills.
If we must jump to conclusions and assume motives in others, the better route to take would be to give someone the benefit of the doubt and assume that they mean well. Something much easier said than done.