Our Gemara on Amud Aleph quotes the verse which describes what the Nazir must perform in order to recover and restart his Nazirhood, subsequent to becoming exposed to a corpse (Bamidbar 6:9):

וְכִֽי־יָמ֨וּת מֵ֤ת עָלָיו֙ בְּפֶ֣תַע פִּתְאֹ֔ם וְטִמֵּ֖א רֹ֣אשׁ נִזְר֑וֹ וְגִלַּ֤ח רֹאשׁוֹ֙ בְּי֣וֹם טׇהֳרָת֔וֹ בַּיּ֥וֹם הַשְּׁבִיעִ֖י יְגַלְּחֶֽנּוּ׃

If someone dies suddenly nearby, defiling the consecrated hair, the [nazirite] shall shave the head at the time of becoming pure, shaving it on the seventh day.

Rav Avraham Yitschok Shein in his Sefer (Shemu’a Yaffa, Nasso) notes that the order of the verses are disjointed. One would expect that the Torah would first detail the procedure for a regular Nazir, his initiation, rules of conduct, and concluding sacrifices and rituals. Instead, the Torah first discusses the regular Nazir’s initiation and rules, then interrupts with a discussion about what to do if he is defiled by a corpse and its various rituals and sacrifices, and then resumes with the discussion of the routine Nazir and its sacrifices brought upon completion.

Rav Shein suggests the Torah is emphasizing that the path to spiritual success is fraught with potential pitfalls. Even though these pitfalls are a setback and necessitate a resetting of the counted days, they are also to be expected. One should not despair or lose heart. 

Persons in Twelve Step programs count their days of sobriety, and honor the attainment of certain milestones, such as 90 days or one year.  Can you imagine how difficult it is to come back to a meeting, after having been two years sober, to announce, “I am one day sober.”? Yet, people who seriously work the program do have setbacks and are able to be honest and face their peers as they restart their sobriety. 

Looking at it scientifically, we are by necessity, under a strong influence to maintain patterns.  The human organism follows patterns to conserve energy by allowing for thoughts and behaviors to operate on auto pilot. The Nazir, like others who want to make changes in life, resolves to make a break from his typical thoughts and behavior patterns.  He is pushing back against his system, and systems will resist change. It is important to be realistic about the process of change and it’s inevitable challenges.  Setbacks are serious but also routine.