Originally authored on May 10, 2018, on Quora - https://www.quora.com/Didnt-Muhammad-say-only-1-out-of-73-sects-go-to-heaven-and-the-rest-to-hell-What-chances-have-you-got
Yes indeed he did say that but he also identified the saved group so that Muslims would not be left in confusion as to which group it would be. In order to clarify this apparent confusion we would just need to understand the following 3 traditions that mention this subject of seventy three sects among his followers. After reading everything shared one can understand that the saved group has always been majority among Muslims and the ones that Prophet ﷺ said will enter hell have always been in minority.
The first tradition appears in the collection of Ibn Majah:
It was narrated from ‘Awf bin Malik (r.a) that the Messenger of Allah ﷺ said “The Jews split into seventy-one sects, one of which will be in Paradise and seventy in Hell. The Christians split into seventy-two sects, seventy-one of which will be in Hell and one in Paradise. I swear by the One Whose Hand is the soul of Muhammad, my nation will split into seventy-three sects, one of which will be in Paradise and seventy-two in Hell.” It was said: “O Messenger of Allah, who are they?” He said: “Jama’ah (The main body).” (Sunan Ibn Majah 3992) 
The second one is recorded by Imam Tirmidhi in his collection similar to the above except for slight difference in the wording identifying the saved group:
Narrated 'Abdullah bin 'Amr (r.a) that the Messenger of Allah ﷺ said: "All of them are in the Fire Except one sect." He said: "And which is it O Messenger of Allah?" He said: "What I am upon and my Companions." (Jami at-Tirmidhi 2641) 
In a third tradition the Prophet ﷺ even identified as to who will be those that will become the cause of divisions in the following words: “…and one of them will go to Paradise, and it is the majority group (jama'ah).” Ibn Yahya and `Amr added in their version : “There will appear among my community people who will be dominated by desires like rabies which penetrates its patient”, Amr’s version has: “penetrates its patient. There remains no vein and no joint but it penetrates it.” (Sunan Abi Dawud 4597) 
The wording in the above traditions that distinguish the righteous from the wrong also teaches few but very important points of guidance.
What does the Prophet ﷺ mean by "Jama'ah or The Main Body"
The main body (Jama’ah) can be observed by the fact that will never be separated from the consensus on religious matters agreed upon from the time of the companions. As the scholars says that to know whether a doctrine or practice is orthodox or heretical, the Muslim is required to find out whether it is recognized by majority or main body of Muslim scholars. This is also corroborated by the fact that the Prophet ﷺ himself clarified that the main body or majority will never agree on an error and will always unite on guidance. Additionally he also claimed that such people of guidance will always prevail over those of misguidance.
Narrated AbuMalik al-Ash'ari, The Prophet ﷺ said: "Allah has protected you from three things: that your Prophet should not invoke a curse on you and should all perish, that those who follow what is false should not prevail over those who follow the truth, and that you should not all agree in an error.” (Sunan Abi Dawud 4253) 
What does the Prophet ﷺ mean by "What I am upon and my Companions"
It is a known fact that companions were the first to have learned Islam directly from the Prophet ﷺ and then the rest of the generation up till today have learned guidance from their example and way. The first ones to learn directly from the Companions were those of the second generation, also called Taba'een (students) who when learning never discriminated among the Companions. Then appeared the ones to learn from second generation were those of the third generation also called Taba Taba'een (students of the students). These first three generations of Islam built the foundation of religious principles for all subsequent generations to learn from. These three generations as per Prophet ﷺ himself are the best in following the teachings of Islam and historically these were the best in teaching and from whom upcoming generations have looked upon for guidance. This is corroborated by the following Prophetic tradition:
Narrated Abdullah, The Prophet ﷺ said, "The best people are those of my generation, and then those who will come after them (the next generation), and then those who will come after them (i.e. the next generation), and then after them, there will come people whose witness will precede their oaths, and whose oaths will precede their witness." (Sahih al-Bukhari 6429) 
After the third generation corruption began to appear at a much wider level when it came to teaching of Islam and knowledge dissemination, therefore then the righteous scholars and saints among subsequent generations continued to follow the methodology of the first three generations and disseminated correct teachings. The majority of these people and their scholars are always found to be part of main orthodox school that everyone refers to as Sunni Islam or Sunnis. Just by observing the fact that all famous Imams who followed the earlier generations for the past 14 centuries, whether from the main 4 schools of thought (Hanafi, Sha’afi, Maliki, Hanbali), all the Imams who collected Hadith, all Imams famous for being Quran commentators and majority of Imams of the Sufis belonged to the school of Ahle Sunnah Wa’al Jama’ah (People who follow Prophetic path and main body) or Sunni Islam. This is an undeniable historical fact of Islam.
Misguided groups and some of their characteristics
One major characteristic of such groups is that their teachings are in clear contradiction to consensus of the past generations and they are almost always a minority among the Muslims therefore its easy to identify them. Many examples of these groups are found in the past as well as in our times.
A good example is found in the fanatics of early Islam during the Caliphate of Ali Ibn Abi Talib (r.a) who are referred to as Khawarij. In their extreme interpretation they were easily identifiable that they were not on the path of the Prophet or Companions. An example of similar group is also the Hashashin (Ismailies) an offshoot of Shias who were fanatics in their expression of Islam and they acted more like cult. An expression of this type is found today in groups like Al Qaeda and ISIS.
Then we have groups who have claimed divinity for Ali Ibn Abi Talib (a.s) and for many Sufi Imams such as Shaikh Abdul Qadir Jilani (r.a). They assign almost divinity to these great persons which Quran and Sunnah does not permit for anyone except Allah ﷻ.
There are also groups that had Imams who claimed prophet hood for themselves an example is the likes of Bahaullah and Mirza Ghulam of Qadiyan. The followers of Bahaullah and Mirza Ghulam claim their leaders were Prophets of Allah ﷻ after Muhammad ﷺ and Islam clearly teaches that there is no Prophet after Muhammad ﷺ but he did warn us against several false prophets that would emerge from within his Ummah.
Then we have those who under the influence of modern Western thought have begun to reinterpret the text to such an extent that they claim there is no need to follow traditional methodology adopted for generations and all of that agreed upon for centuries was misguidance. Their examples are found among those who claim that "hadith is to be rejected and only Quran is sufficient". A good example of this type is also found in the group in Western countries claiming that women can act as Imams for mosques and even lead men in prayers. Additionally they also claim that men and women can pray side by side like men and no need to have separation. These types of beliefs clearly contradict teachings of Quran and Sunnah and the way of Companions and those who followed them. Some have also adopted a racist stance and interpreted that Islam is a "religion of black people" such as Nation of Islam in USA and they have also deviated from the truth.
To know more about the jama'ah (the main body) from authentic Islamic teachings there's a very good article by Shaikh Ahmed ibn Muhammad: Who are the Ahl as-Sunnah wa'l Jama'ah?
Last but not least we need to always keep in mind the saying "hate the deed and not the doer". The misguidance that many followers of misguided groups follow may be doing so out of ignorance and not willingly and therefore it could be that many are forgiven by Allah ﷻ who judges everyone through their intentions.