Deviation from the correct Aqeedah has many causes, from the most important of them are:
1. Ignorance of the correct Aqeedah due to turning away from learning and teaching it or lack of concern for it -until there arises a generation who is ignorant of the correct Aqeedah and that which contradicts it. The truth is then deemed to be falsehood and falsehood to be the truth -as Umar Ibn Khattab said, "Verily, the bonds of Islam will be destroyed one by one, when there arise in Islam people who do not know or recognize Jahiliyah (ignorance).”
2. Bigotry (ta'assub) towards the beliefs of the ancestors -adhering to them even if they are false and forsaking everything that opposes them even if it is the truth.
Allah says, "When it is said to them, 'Follow what Allah has sent down.' They say, 'Nay! We shall follow what we found our fathers following.' (Would they do that!) Even though their fathers did not understand anything nor were they guided?' [Soorah al-Baqarah (2): 170]
3. Blind-Following (Taqleed) by accepting people's statements concerning Aqeedah without knowing the proof or level of authenticity -as is the case of the Jahmiyyah, Mu'tazilah, Ash'aris, Soofis and others whereby they (blindly) followed their deviant scholars who preceded them and thus, they were misguided and went astray from the correct beliefs.
4. Extremism or Exaggeration (in honoring) the Awliya (saints) and the Saliheen (righteous) through the following acts Raising the Awliya and the Saliheen above their due status where it is believed that they bring benefits and prevent harm in a manner which none has the ability to do except Allah.
Taking the Awliya and the Saliheen as intermediaries between Allah and the creation in fulfilling needs and answering the duaa -until the matter turns into worshiping other than Allah.
Seeking nearness to their tombs through sacrifices, vows (nadhr), supplication, seeking aid and asking for help like what occurred among the people of Nuh regarding the pious. They said, "You shall not leave your gods, nor shall you leave Wadd, Suwa, Yaghuth, Ya'uq nor Nasr (names of the idols).” [Soorah Nuh (71):23]
Such is also the case of the grave-worshippers of today in many countries.
5. Negligence in pondering over the universal and Qur'aanic Ayaat (proofs, evidences, verses, lessons, signs, revelations, etc.) of Allah while being overwhelmed by the facts and figures of the material civilization -until people think that this is from man's ability alone. They glorify man and attribute these accomplishments to man's endeavors and experiments alone -as Qaroon said, "This has been given to me only because of knowledge I possess." [Soorah al-Qasas (28): 78] and as man says, "This is for me (due to my merit)." [Soorah Fussilat (41): 50] "Only because of knowledge (that I possess) I obtained it." [Soorah az-Zumar (39): 49]
They do not ponder or look at the glory of the One, Who originated this universe and bestowed in it these magnificent wonders. He Who originated man and conferred upon him the ability to derive and utilize these benefits. "Allah has created you and what you make!" [Soorah as-Saffat (37): 96] "Do they not look in the dominion of the heavens and the earth and all things that Allah has created." [Soorah al-A'raf (7): 185]
"Allah is He, Who has created the heavens and the earth and He sends down water (rain) from the sky and thereby brought forth fruits as provision for you. He has made the ships to be of service to you – so that they may sail through the sea by His Command.
He has made rivers (also) to be of service to you. He has made the sun and the moon -both constantly pursuing their courses -to be of service to you. He has made the night and the day to be of service to you. He gave you of all that you asked for and if you count the Blessings of Allah, never will you be able to count them." [Soorah Ibraheem (14): 32-34]
6. Houses have become empty of the correct guidelines. The Messenger of Allah said, "Every child is born upon Fitrah (natural inborn instinct which recognizes Allah) but his parents make him a Jew, a Christian or a fire-worshiper." [Agreed upon] Parents thus play a big role in setting right the child's way of life.
7. Lack of importance for the means of teaching and spreading (Islamic) knowledge in most of the Islamic world. More often, the methods of teaching do not give much importance to the religious part or they are careless in this regard from the start.
The means of transmitting knowledge whether textual, audio-visual or verbal have mostly become tools of destruction and misguidance or they are more involved in material and entertaining obsessions. People do not care about building (good) character, instilling the correct Aqeedah or combating misguided trends until there arises a generation who is defenseless against misguidance.