Yes, emotions can be controlled. Controlling emotions doesn't
mean hiding it. Negative emotions, no matter how good you hide it,
will definately affects your judgement and also cause harm to your
mental and physical health. The best way is to reduce all these
negative emotions to the minimum.
If anyone of you is interested, there is a book written by Anthony
Robbins, tittled "Awaken the Giant Within".
In this book, there is a certain section which teach us how to
shift our emotions from negative to positive. I'm now trying one of
the exercises in this book called the 'mental diet', which means
that in 10 consecutive days, whenever anything happen which will
cause aniety, anger, depression,etc., i have to immediately shift
these negative mental states to positive ones. This exercise is
really tough, i have been trying it for more than a month liao but
still haven succeed yet.
Actually emotions is easily reinforced. If one repeatedly gets
irritated, the mind will be so used to this emotion. So when little
things happen, the mind will automatically searches for the most
familiar emotion to match.