Be not discouraged if you do not succeed at everything

 Be not disgusted, nor discouraged, nor dissatisfied, if thou dost not succeed in doing everything according to right principles. But when thou hast failed, return back again, and be content if the greater part of what thou doest is consistent with man's nature.  Marcus Aurelius.  Meditations.  Book 5.

Image: Statue of Ambiorix, prince of the Eburones Belgic tribe of northeastern Gaul, in Tongeren, Belgium courtesy of Wikimedia Commons contributor I, ArtMechanic (sky added using Photoshop's phenomenal sky replacement tool)..  

Ambiorix ambushed and destroyed one of Caesar's legions under the command of Quintus Titurius Sabinus and Lucius Aurunculeius Cotta near Atuatuca Tungrorum (modern Tongeren, Belgium) in 54 BCE during the Gallic Wars.

When the Roman Senate heard what happened, Caesar swore to put down all the Belgic tribes. The Roman campaigns against the Belgae took a few years, but the tribes were eventually slaughtered or driven out and their fields burned. The Eburones ceased to exist following the campaign.

Historical novelist S.J.A. Turney does an excellent job imagining the battle and the aftermath in his books, Marius' Mules V, Hades' Gate and VI: Caesar's Vow.