Well comparing sith to real life people is a bit unfair since the force doesn't exist in real life. Dark side of the force is powered by your emotions, the more emotional you are the stronger you get, although it is just as easy to lose control over that power and become an ignorant, pridefull, idiot which, is the sith downfall they use their emotions to fuel their strenght, but eventually get too pridefull and die because of it or get mortally injured (Anakin).
However that generally happens with sith who are new and more rash, the key is like a lot of people mentioned before me is to control those emotions. Fear is the most basic and the easisest emotion that you can feel so, whether you like it or not nearly all sith feel fear. At first from their masters and/if they become a master from ther aprenticesses or other masters, this keeps them focused and constantly watching their backs.
Anger is the gateway to hatred which can be directed towars a lot of things, towards the enemy, towards weaker sith, even towards the sith himself/herself it doesn't really matter though, as long as there is enough emotion it is fine. You can compare it to a boxer receiving a pep talk from his coach before a match but in this case emotions are not only a drive but, also the fuel for the dark side which the sith will use.
You are taking the subject of anger as we normal people do, our bodies produce adrenalin we stop getting tired but become ragefull and lash out to, eventualy get exhausted after putting our bodies through an unnessecary ordeal but, it isn't the same with sith it is more of a constant thing, they always feel anger, always feel fear and hatred, these empower them they also corrupt them and deform them in some ways, of course there are exceptions to this but im not going to disscuss them here, what i wanted to say was in essence the anger that we feel as real people is different than what the sith feel. It is more like achieving control over your anger and channelling it to a certain object or person. I guess what im trying to say is it is a means to an end not the end itself.