Imagine fighting a powerful enemy for decades, keeping him at bay. And then, abandoning this working strategy. Gambling everything on one single battle - a battle that ends not only in annihilation of your army, death of your ruler, but also utter collapse of the defenses, and loss of most of your country.
Not only the loss of territories but also the very loss of your sovereignty, for centuries, with your lands becoming part of the other realm.
That is what happened at the Battle of Mohacs, on August 29, 1526, where one battle, in less than three hours, changed the fate of the Kingdom of Hungary for good. And the fate of (Central) Europe.
With the Ottoman Turks taking most of the country, including the capital of Buda (liberated in 1686), and the Austrian Habsburgs becoming new rulers, until 1918.