Our Gemara on Amud aleph makes an observation about human nature and that certain sins are almost impossible to avoid:

The majority of people succumb to sin with regard to financial dishonesty and theft, and a minority of people succumb to sin with regard to sexual matters, and everyone succumbs to sin with regard to malicious speech. The Gemara asks: Can it enter your mind that all people sin with regard to malicious speech? The Gemara answers: Rather, Rav was referring to uttering that is close to (avak) of malicious speech.

The Hebrew word for “close to” is avak, and more appropriately translates as dust. It used to metaphorically convey a sin that is at least in spirit of a similar moral breach, though may not be technically as forbidden. For example, rabbinically prohibited usury is known as avak ribbis.

The Panim Yafos (Vayishlach) notes that Yaakov’s wrestling with Esau’s guardian angel was described as Vayeavek (Bereishis 32:25). This has the same linguistic root as avak dust, possibly because when people wrestle, dust flies, as in the English idiom, “to get dusted up.“  He says Satan did not have the ability to overcome Yaakov by causing him or his descendants to sin explicitly, however he was able to make inroads regarding practices that were dubious and morally questionable, but also possible to rationalize. That is why the Torah uses a word that hints at dust.

Reflecting on this, we might also consider the Noam Elimelech’s (Vayishlach 6) interpretation of this dust and the ultimate shining of the sun that happens at the end of the episode (ibid 32). Just as dust obscures, on some level Yaakov was undergoing confusion and a resulting lack of faith. The Midrash says that the dust of this battle rose up to the heavenly throne. The meaning is that his confusion affected Yaakov's ability to connect to God, but he eventually emerged victorious from his struggle, which is represented by the sun shining in the morning. He eventually came to a place of moral clarity.

When something is clearly forbidden we still may have tests and challenges of character, but it is much harder to overcome temptation when we also feel a lack of clarity. If a sin is subtle, we are more likely to rationalize it. This could be another reason why certain sins are described as avak, because they come from a blurring and confusion and it takes time for the dust to settle and develop moral clarity.