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There are roads which must not be followed, armies which must not be attacked, towns which must not be besieged, positions which must not be contested, commands of the sovereign which must not be obeyed.

Sun Tzu, Julius Caesar, Einhard, Niccolò Machiavelli, Carl von Clausewitz (2016). “Strategy Six Pack”, p.19, Lulu.com
There are roads which must not be followed, armies which must not be attacked, towns which must not be besieged, positions which must not be contested, commands of the sovereign which must not be obeyed.