In this week's parsha the Torah relates the story of the spies in great detail. Included in the narrative is an account of their travels through the Land of Israel: "And they ascended in the south, and he arrived at Chevron" (Bamidbar 13, 22). Rashi explains that although all the spies entered into the south, Kaleiv was the only spy to arrive at Chevron. He purposely made this detour since he wanted to daven at the burial place of the forefathers that he not be convinced by the other spies to join their scheme.
Rav Wolbe (Shiurei Chumash) comments that it is difficult to understand the impetus for Kaleiv's detour. If he was aware of the fact that the spies were scheming, and he knew that he didn't want to join them, why couldn't he simply decide not to agree to their plan. Why did he feel the need to visit Me'aras HaMachpeilah to daven that he achieve what he had already determined was the proper course of action? Why wasn't a firm resolution enough to prevent him from being lured into their plot?
The answer is that one should never rely on his bechira (free will) when faced with the possibility of transgression. He can never be sure that he will indeed make the correct decision, and, therefore, he should always perceive himself as if he has no bechira at all and will certainly succumb to the aveirah. Such a mindset will push him to do everything in his ability to prevent himself from entering the problematic situation in the first place lest he falter and transgress. Kaleiv didn't want to rely on his own resolution not to join the other spies, and therefore he prayed for Heavenly assistance that he not be convinced to join them.
Often, we visit places, speak to certain people or bring items into our houses that have the ability to cause us spiritual damage. We excuse these actions with our confidence that, due to our steadfast morals, we won't be affected negatively. However, truth be told, this is not the proper approach. Our avodah is to do everything possible that we not have to face a nisayon in the first place. This is the best way to ensure our spiritual success.