Mishnah Berurah — משנה ברורה

In vain - Even though without this (ie. without checking the strings) there is a concern for the [following] prohibition: that he will wear a four cornered garment without ציצית... nevertheless, we establish that there is a presumption that it (ie. the garment) was valid; [But] only because of the stringency of [the prohibition of] "You shall not swear falsely [by the name of the LORD your God]" which exists on a blessing made in vain, they were stringent that one should check them. According to this, one who is wearing multiple garments that have ציצית only needs to check one of them, since only one blessing is made over all of them. However, the later authorities wrote that one needs to check them all: Firstly, because we don't rely on a presumption in a place (ie. situation) where you are able to clarify [the matter]; And additionally, [in this case] it is an inferior presumption... for strings are easily severed. Therefore, one must check [them] everyday in the morning when he wears them... and then, even when he removes them and takes his mind off of them... even though he is required to make a blessing on them when he wears them again... even so, he is not required to check them again for in a short span of time like this they are not normally severed and we can rely on the presumption. And even in the morning... if by checking [his ציצית] he will miss out on praying with the congregation, or if he got called up to the Torah... he may wear his טלית without checking it. And this is when he knows that the strings were intact the day before. Nevertheless, it is proper for him to check them as much as possible. And if he borrowed a טלית from someone else to go up to the Torah, [in which case] our custom is to not make a blessing on it (ie. we don't make a blessing on a טלית when getting called up to the Torah), he does not need to check it at all [and see further in Biur Halacha[5]]. And if he checked the טלית when he removed it and placed it in its pouch, he does not need to check it again tomorrow when he wraps in it.