toddler wishes and tantrum dreams

What is reasonable behavior for a four-year-old? If you give him a piece of toast, with butter that has melted into the bread, because its toast, and its hot; is it normal that he immediately starts screaming that he needs MORE butter? He apparently needs to be able to SEE the butter, unmelted and thick and disgusting in order for it to be appetizing. I tell him over and over that there is, in fact, butter on his toast but he is unconvinced. The next 7 minutes of my life are filled with so much drama you would think he had suffered a severed toe. Is this normal? How can a four-year-old get just as upset over butter as he might get over suffering a major injury. Then I wonder, is it just manipulation? Have I taught my kid that if he cries loud and long enough he will eventually get what he wants? I guess the obvious answer is yes because as soon as I let him add a tiny bit of butter to his toast, he was miraculously cured. How do they do it? I am supposed to be the older and wiser of the two of us. Yet, he is the one that is able to get what he wants almost all of the time. Sometimes I wish that if I cried loud and long enough, I could manipulate my kids into doing what I want. Will screaming and throwing a tantrum get them to unload the dishwasher for me, or get them to make their beds? I doubt it. But I guess that is parenting. As much as I want to throw myself on the floor and act like a toddler out of control, I can't. I have to "model" appropriate behavior; stinkin' parenting classes, ugh.