David went out wherever Saul sent him, [and] behaved himself wisely: and Saul set him over the men of war, and it was good in the sight of all the people, and also in the sight of Saul's servants.
He set up a dowry regarding the Philistines. David went out and gave him double dowry. So Saul then of course was sort of shocked and surprised. He figured David would get wiped out in going out against the Philistines.