Qitzur Shulchan Arukh – 67:5
Someone who makes nedarim in order to fix his middos, he is proactive and praised. How? If he was a glutton, and swore that he won’t eat meat for a certain time. Or if he was an alcoholic, and prohibits wine and other intoxicating drinks. And similarly someone who was prideful of his appearance and accepts upon himself nazarite laws. And the like. Nedarim like these are the service of Hashem, may His repuration be blessed, and about these our sages of blessed memory said, “nedarim are a fence around separation [from temptations one can not resist].”
And sin all cases even in nedarim like these, it is not for a person to habituate himself [in them]. Rather, he should overpower his [negative] inclination even without nedarim.
I invite people to comment on my translation of “perishus” as “separation [from temptations one can not resist].” It should really be something more like “doesn’t reliably resist”, but the entire line of thought isn’t a given. How would you define “perishus“?