The level of obligation of statements in the Gemara and customs

In my personal opinion, this does not have much validity. Even in the language of the poskim, one should pay attention to whether they write this as a complete obligation or as a recommendation, custom, etc. Some poskim do not make the effort to make these distinctions (like the Kitsush'a).
Ultimately, the validity of all of these is by virtue of custom and not because one or another rabbi wrote it.
The same goes for Shacharit. The custom today is to do everything. 
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Asks:
Regarding head covering and prayer, it is clear that this is the true custom. But is there a custom to put on the robe (or any garment) the way it is (and not the other way around)? How do we determine whether this is indeed a custom? The same applies to wearing the robe (or any garment) under a blanket.
Is it correct to say that the obligation from a custom is only in action (the kippah, the form of the prayer, etc.), and not in non-action (not dressing outside the blanket, not putting clothes on inside out, etc.)?
 
Beyond this, there are customs that are practiced but are not halachically binding – donuts on Hanukkah, costumes on Purim, the wearing of tefillin/mezuzah, halaka, atonement rooster, etc. What is the criterion for distinguishing between halachically binding customs and those that are not?
 
And above all, why is a custom (which is not an ancient custom but a new one) binding at all (and isn't there a reason for not adding anything to it?)
 
I saw several sources online for the voice:
In an article taken from the words of Menachem Alon:
 
I think that since the majority of the Jewish people do not observe Halacha, customs do not have a binding meaning, as they did in ancient times.
Many customs are today considered a halakhic obligation, and any person who thinks that something is forbidden, when his mistake becomes clear, will be able to cancel his custom. 
 
Additionally, in the Tosafot Tractate Avoda Zara, page 95, page 1, it is written: "If the halakha in your hand is loose, follow the custom," implying that where the halakha in your hand is not loose, there is no obligation to follow the custom.
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Rabbi:
1. I didn't understand the question. What does it mean, how do you measure whether something is a custom? If it has a source – then it is a halakha, and if not – then it is at most a custom.
2. A custom that those who practice it themselves understand is not obligatory is a non-binding custom. These are donuts and the like.
3. What is the difference between an ancient custom and a renewed custom? Every custom was once renewed and after a while will be ancient. Customs that are learned from either the law of a vow or from the verse "Do not forsake the law of your mother" are valid (see the beginning of the verse, where they were practiced on Passovers). According to the Maimonides, there is a "bel t'sif" only if it is said about something that is from the Torah. Not everything that is practiced is a "bel t'sif". Therefore, he writes that sages who correct or decree should indicate that this is their legislation and not the law of the Torah.
4. In my opinion, the fact that most people do not observe halakha is meaningless. There were other periods when most people worshipped idols. So what? What matters is what those who are obligated to do do. And in general, a custom does not need to be observed by all of Israel. There is a local custom, a denominational custom, and the like.
5. Regarding a person who was mistaken and thought it was a halakhah and it was clarified to him that it was a custom, there are jurists who permit this even without the permission of vows. I am not sure about this.
6. The words of Tos that you cited are an explicit Gemara in Yerushalmi in several places (see Paha 57:55 and more). The meaning of these words is that there are two types of custom: 1. A neutral custom (not halakhic), such as the sufganiot or the kippah. It is valid by virtue of "do not neglect," and so on. 2. Halakhic custom (it is customary to rule on halakhic law in this way and not otherwise). The second custom deals with the ruling of halakhic law, and after ruling in this way, it is binding because it is the halakhic law and not because of "do not neglect." This is just a rule in halakhic law, that if you do not know, you follow the custom. And this is what Yerushalmi says. Therefore, it is clear that when you know what the halakhic law is, there is no reason to follow the custom. But this is only in type 2 custom, and not related to type 1 custom. Of course, type 1 custom does not uproot halakhic law either.
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Asks:
1. I meant how do you determine that something is a custom? I assume that there is some kind of blurred boundary and let's say the custom of covering the head is deep in the realm of custom, the question is about borderline cases of all kinds of esoteric customs that quite a few people are not familiar with at all. In other words, what is the criterion for determining whether something is a custom or not in cases where it is not obvious.
2. Regarding understanding, it may be clear to others which custom is binding and which is not, but to me it is not so obvious, so I am trying to understand how to distinguish between the two. There are also rabbis who are strict in the Torah about binding customs that other rabbis consider non-binding, and then the question arises, who should we believe?
3. Regarding an ancient custom, there is at least a possibility to say that it is a custom that originated in Sinai and that it preserves a forgotten halakhic matter, but regarding a renewed custom, this certainly cannot be said. 
4. The question of whether a person who is not part of any community, and whose ancestors did not leave him a legacy of obligatory customs (for example, legumes on Passover), is he obligated to any customs, and if so, whose customs.
6. If I understood you correctly, the validity of the custom of donuts, for example, is by virtue of "do not throw away," so why wouldn't it be binding? And if it is not binding, then is it possible to conclude that all other customs that are not halakhic are also not binding to the same extent?
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Rabbi:
1. Things that some people do are not a custom except perhaps for their community (if it is a defined community). The burden of proof is on the one who claims that something is a custom. There is no clear criterion, and common sense is used (as with everything).
2. See 1. The question of the rabbis is no different from any halakhic question about which there is controversy. If you are a bar, you should enter into the matter and decide for yourself. If not – find a rabbi. By the way, I think that usually when you ask the rabbis whether in their opinion this is a halakhic or custom and whether it is binding, they will answer you matter-of-factly.
3. A custom is not a law that has been lost to us. It is an innovation by definition. An ancient custom is no more credible in my opinion than a new custom, except that if it has spread throughout the general public then it is binding according to the law of custom. Of course, this depends on which of the two types of custom I defined in the previous email we are dealing with.
4. No. Only customs of all of Israel.
6. Because donuts, even those who practice it will tell you that it is not mandatory. I also practice reading interesting books, and so do I assume most of my community members. Is this becoming a custom in my community? The same goes for eating cottage cheese for breakfast.