Interesting topic and generally speaking I'm on Camarada's side but I think it's a bit more complicated. Humans make self protective decisions based on emotions and experience of emotions automatically and generally not through choice. I would argue that even these decisions are not consciously controlled by yourself but just formulated as a result of previous experiences, not just the original experience but a combination of many others possibly even ones such as reading this forum. The illusion of control over everything you do is one that neuroscientists are currently proving to be a fallacy as the desicions are made and your conscoius will justify it afterwards making you beleive it was your choice.

Therefore the only way to control emotions is to have been in the situation previously and have a reference point or exposure to a defense mechanism which gives the illusion of control, when in fact it's decision made before you consciously try and control it.

Basically everything you think or do is just an automatic reaction based on experiences and environment and not controlled, the belief you have control over it is just a backwards rationilisation.