Nedarim 12: Keeping our Vows

I found today's daf to be more confusing than most - well, most of our more recent dapim. It seems that an intricate knowledge of the legal concepts is almost required.  

Steinsalstz's commentary suggests that today's daf is part of our larger understanding of stating vows. There is a principle that defines how vows must be stated.  In part, the practice of one's vow must be compared with something else - this object is forbidden to me like a sacrifice, or like Jerusalem, etc.

Along with comparisons, people can make vows that use phrasing of "like the time that".  For example, I will fast like the time that my father died.  The rabbis follow one example of vow regarding "fasting like the day my father died".  Did this vow mean that the 'mourner' would fast every year on that date?  Or only on the years that the actual date of death fell on a Sunday, the day of the week that the father died?

The rabbis note that people did fast to mark yartzheits, but that this act was sometimes a vow and sometimes simply a minhag, a custom.  People followed that minhag in many communities with more rigour than other minor fast days.  The rabbis speak of the tension between Biblical halacha and minhag.  Today we continue to understand the importance of observing halacha - with its own, more severe consequences - and observing minhagim, with similarly stringent social costs attached to non-adherence.