But for many backbench MPs yesterday, following that mantra became a rather difficult task.
They knew that the bad guys were the group sitting opposite them.
And yet their leader was doing something often talked about but rarely seen.
He was agreeing with, whisper it, the opposition.
Worse, he was agreeing that they should all turn down something that most members of the public would kill for - a whopping 11% pay rise.
Perhaps this was what led to a rather subdued tone at Prime Minister's Questions.
That, or MPs were still reeling from last week's news that, like the rest of us, another day at the office was nothing compared with the couple of hundred more they can now expect before they get their state pension.
David Cameron still managed to be animated, however, as he fought off questioning from Labour.
He did appear to struggle at times, though, also to know who exactly his enemy was. Casual observers would be forgiven for thinking that the Prime Minister has managed to grasp only that the winner of the Labour leadership contest was called Ed.
Such does his attention flit between Mr Miliband and the shadow Chancellor Ed Balls.
Confusingly, even a crack that the Labour frontbencher would soon to be replaced in his job was directed at, er, both of them. Mr Cameron also forgot to be wary of all Labour MPs when the Glasgow politician Tom "Bomber" Harris thanked the Prime Minister for saving his marriage through the married couples tax break.
The Tory leader for a second looked genuinely pleased at the thought of having brought harmony to the Harris household.
Until, that is, Mr Harris innocently asked why in the years since the marriage tax had been abolished had divorce rates gone down?
So there you had it. The true enemy of the Conservatives' policies: marriage guidance counsellors.