Because the frontal cortex and all that rationalising nonsense that seperates us from the animals wants to keep control, whilst your inner being, that amygdala and other such more gorilla like parts of you want to tear people's arms off when you are angry, or because you know if you start crying you won't stop for a long time. The thing is you need to let the emotions out or they will grow into figurative demons inside you, but because you have been keeping a lid on it so long you are afraid to let them out because instinct tells you that anything could happen. I think the trick is to get a balance between the two and not be all or nothing. Let the emotions out as close to the time that they occur as possible, and do it in little doses so that it doesn't overwhelm and then take the control back. But it is all you. It is all valid. And there is nothing wrong with how you feel and you can know that because you are feeling it.