Full Idea
An official could turn a person back from an unsafe bridge without infringeing their liberty; for liberty consists in doing what one desires, and he does not desire to fall into the river.
Gist of Idea
Blocking entry to an unsafe bridge does not infringe liberty, since no one wants unsafe bridges
Source
John Stuart Mill (On Liberty [1857], Ch.5)
Book Reference
Mill,John Stuart: 'Utilitarianism (including On Liberty etc)', ed/tr. Warnock,Mary [Fontana 1962], p.229
A Reaction
Seems fair enough, but it justifies paternalist interference. The tricky one is where the official and the citizen disagree over what the citizen 'truly' desires. Asking people may involve too much time, but it could also involve too much effort.