Any experienced courtroom lawyer knows you never ask a question that you don't know the answer to.
The equivalent for a politician is to avoid setting up inquiries where the outcome could make things worse than the original problems.
Simon Bridges is an experienced courtroom lawyer and politician.
For that reason it has been inexplicable from the outset why he decided to push for an inquiry over who leaked details of his travel expenses - a few days before the public disclosure.
From the moment he called for an inquiry, he lost control of the situation. And the revelations today of a supposed anonymous confession and plea-cum-threat not to pursue the inquiry compounds that.
Bridges clearly judged that the perpetual uncertainty of not knowing whether the leak had come from one of his caucus was worse than perhaps knowing it had.
It was an uncertainty that Bridges' opponents were using to damage him - and undermine his leadership.
He also invited a level of snooping into MPs' and staff computers quite disproportionate to the original offence. It was an overreaction.
The risks for damage now are far greater than they were at the outset.
It was evident from this morning's press conference about the anonymous confession he received that he does not know if he is dealing with someone who is genuinely threatening to hurt themself if they are exposed through the inquiry, or someone who is cynically issuing threats to avoid being caught.
He cannot tell if it is an MP or a staff member.
The decision by Speaker Trevor Mallard to confirm the inquiry and name the QC conducting it shows firmly where he stands.
He is not going to bow to anonymous threats from the leaker. Bridges is saying the same thing but in a slightly gentler way.
Mallard and Bridges are right. It would be improper to stop the inquiry on the basis of the threats received. That is blackmail.
The astonishing, but slightly comforting, fact that Bridges revealed today is that police now know who that person is - at least the person who claims to be the leaker.
The police will have their own procedure and protocols around who may be informed of the facts of the case and for what reason - and that should be respected.
One thing is certain: while Bridges lost control of the situation long ago, the culprit must have a sense of their world spiralling completely out of control - knowing the police are involved and that the QC is about to find out one way or another very soon.
A proper confession may be the quickest way for that person to regain control.