In Likutey Moharan II, 44, the Rebbe cautions us not to be overly stringent in any observance. The Rebbe quotes the Talmudic maxims, “God does not rule over His creatures with tyranny” (Avodah Zarah 3a), and, “The Torah was not given to the ministering angels” (Berakhot 25b; see “His Wisdom” #30).
The Rebbe also said, “It is written that every person should choose one observance and keep it strictly with all its fine points. The Talmud alludes to this where Rabbi Joseph asks Rabbah’s son, ‘With what observance was your father most careful?’ (Shabbat 118b).
“Even with this observance, you should not be abnormally strict to the point of foolishness. Certainly, do not let it make you depressed. Simply keep all its finer points without fanaticism.
“Keep one commandment strictly, but others need not be observed with any unnecessary stringency at all. It would be enough if we were worthy of keeping all the Torah’s commandments according to the law, without going beyond it.”
The Rebbe was also very much against all the special stringencies that are observed on Pesach. Many people go so far in observing many fine points of custom that they are literally depressed by the holiday. He spoke about this at length.
One of his followers once asked the Rebbe exactly how to act with regard to an ultra-stringent observance. The Rebbe made a joke of it.
The Rebbe spoke about this quite often. He said that these ultra-strict practices are nothing more than confused foolishness. He told us that he had also been caught up in this and would waste much time thinking up all sorts of unnecessary restrictions.
Once he worried about the drinking water used during Pesach. He was afraid that a small amount of leaven might have fallen into the well from which they drew water. The only alternative would be to prepare water in advance for the entire Pesach week, as some people do. But this also was not good enough, for the water had to be carefully safeguarded from leaven from the day before Pesach, and this was very difficult.
The Rebbe finally came to the conclusion that the only satisfactory water would be that drawn from a flowing spring, just as it emerges from the ground. He could then obtain perfectly fresh water without any possibility of its being contaminated. The problem was that the only such spring in the area was very far from his home. He thought about traveling to a place near a spring and spending Pesach there.
This is an example of how deeply the Rebbe had become involved in such unnecessary strictness. But now he ridiculed this and taught that such ultra-strictness is unnecessary, even on Pesach.
When the Rebbe spoke about this, he continued, “True devotion consists mainly of simplicity and sincerity. Pray much, study much Torah, do many good deeds. Do not worry yourself with unnecessary restrictions. Just follow the way of our forefathers. ‘The Torah was not given to the ministering angels.’
“This is why people no longer study dikduk, the rules of grammar. People have abandoned it because this type of precision is not really necessary. This is true of all areas. You should not be overly precise in seeking out restrictions.”
The Rebbe spoke at length along these lines, concluding, “There is nothing that you absolutely must do and if not … . If you can, fine, but if not, ‘God exempts a person under duress’” (Bava Kama 28b; see “His Wisdom” #14, #27).
 Cf. Emunot VeDei’ot 5:4; Sefer Chasidim 529; Rambam on Makkot 3:16.