This incident shows how a victory which could really be quite worldly and accomplished in carnal strength can have such an effect upon the personality. Although the Ammonites were very belligerent, they were not very big. When you see the enormous number of forces that Saul threw against them – three hundred and thirty thousand – they must have been outnumbered something like ten or fifteen to one. It was really a bit of a pushover, but it doesn't matter: the effect was that, from that moment on, Saul fought like a king, felt like a king, felt like a world-beater, and a true custodian and guardian of the people of Israel in his own strength.
That can often happen to us. We are inadequate for the task, and indeed we are inadequate for most the tasks the Lord lays upon us. Yet it is a simple trick of psychology: if we are inadequate and apprehensive and, we get an easy victory, it goes to our heads, and the next time we do it we are not as prayerful, nor as dependent on the Lord. Sometimes a victory can be more dangerous than a defeat. It certainly was in the case of Saul.