Should someone take on a new stringency/hiddur/optional mitzvah if he or she is not absolutely sure he and his progeny will be able to maintain it on all further occasions? In such a case, is it better to take the risk and rely on G-d's future help in order to grow one's avodah, or not to take such a risk at all?
(It would seem that taking on a new practice by a "bli neder" is the best possible option. However, it's still unclear to me how often one has to say/think "bli neder" in order to retain that status. Is it by every performance of the mitzvah? One in three? When one starts? And if there is a risk of messing up the "bli neder," should one not undertake the mitzvah?)