Dovid did not rely on Divine Promises

 Akeidas Yitzchok (#26): Who was greater than Dovid the anointed king and beloved of G d. Despite the fact that he had promised security by the prophet, he struggled with all his natural ability to save himself from his enemies and from Shaul. He did not rely on the Divine promises because he knew that G d’s rescue and promises does not apply as long as it is possible to be saved by natural means. This is true even if the natural means are debasing such as his feigning insanity and let saliva drip on his beard to escape his enemies. Failure to use all natural means is indicative of laziness. It is only after totally exhausting every possible natural option - and the situation appeared hopeless - do we find that he prayed that G d rescue him