"How to deal with bullies", according to my Dad:

[Bernardo de La Paz]

35. Military say "No plan survives contact with the enemy" but Eisenhower also said

Eisenhower said (paraphrased): "Plans are worthless but planning is everything."

Quote Investigator: In 1950 Dwight Eisenhower wrote a letter to a U.S. diplomat in which he ascribed a military-oriented version of the saying to an anonymous soldier. Emphasis added to excerpts by QI:[1]

. . . I always remember the observation of a very successful soldier who said, “Peace-time plans are of no particular value, but peace-time planning is indispensable.”

During a speech in November 1957 Eisenhower employed the saying again. He told an anecdote about the maps used during U.S. military training. Maps of the Alsace-Lorraine area of Europe were used during instruction before World War I, but educational reformers decided that the location was not relevant to American forces. So the maps were switched to a new location within the U.S. for planning exercises. A few years later the military was deployed and fighting in the Alsace-Lorraine:[2]

I tell this story to illustrate the truth of the statement I heard long ago in the Army: Plans are worthless, but planning is everything. There is a very great distinction because when you are planning for an emergency you must start with this one thing: the very definition of “emergency” is that it is unexpected, therefore it is not going to happen the way you are planning.

They also mention the first saying:

A thematically similar statement was crafted by Prussian Field Marshal Helmuth von Moltke the Elder in 1871. Here is the original German form together with an English translation:[3]

Kein Operationsplan reicht mit einiger Sicherheit über das erste Zusammentreffen mit der feindlichen Hauptmacht hinaus.

No plan of operations extends with any certainty beyond the first encounter with the main enemy forces.