From The Observer: Ministers' loyal guard dogs must always remain invisible | Politics
"Special advisers are like dogs. Loyal and servile to their cabinet minister masters. If their master is sacked or resigns, advisers follow them into the wilderness. One moment they are sitting in a great office of state, lording it over thousands of civil servants. The next, they walk off in an instant and disappear. It's a precarious life chasing triumph but facing disaster, marching on the edge of a precipice.
In turn, ministers choose their advisers as they would a dog. To protect them, but also to provide something they lack – to do things they can't or won't do. A nice, quiet minister may choose an attack dog. A nasty minister may choose a wiser, more affable dog. For the relationship to work, they have to complement each other. Over time they grow together until an adviser can anticipate his master's wishes, words and intentions. It becomes second nature. Like dogs and their masters, they even start to resemble each other, to talk and act in the same way. This can lead to warped judgment, unconditional loyalty and, on occasion, strange, inappropriate behaviour."