Al Imam Al Baqer (a.s) says:” All sins are extreme. The most extreme of sins are those covered with flesh and blood because a servant is either bestowed with mercy or tortured; and only good people enter heaven”. 
Then all sins are extreme because they are considered a disobedience for divine commands and here lies its severity even if some sins are more extreme than others. The most severe among sins is what is covered by flesh and blood, according to the narration, which means sins that include eating from unlawful livelihood and insisting on committing a sin without making amends through repentance.
A man who’s bestowed with mercy is he who makes amends for his sins through repentance or suffer from distress in life. On the opposite side there’s the tortured who is the man who doesn’t make amends for his sins through the mentioned ways; only a good man enters the paradise which means he who is sinless. 
Then, all sins are extreme and they are all great sins. There is no difference between sins because they are all considered as a disobedience for God almighty. They are comparative, not exceptional so we say “small sins” in comparison to sins greater than them, or we say “great sins” in comparison to sins smaller than them. 
An injury is considered small in comparison with killing, but considered great in comparison with slapping. Same as adultery is considered great in comparison to unlawful looks. 
Therefore we understand from the advanced story the need to avoid every sin which is considered a sin in the Islamic law. But we should also prevent every mistake that we assume is a sin, as a respect for the greatness of God and our duty to obey Him. The boldness towards his majesty is possible in that case too. So he who assumes that there’s wine in a glass, should logically not drink it, not only for the side effect of drinking wine, but for the greatness of God and necessity of obeying Him, even in issues with doubt.
Be Cautious of Belittling Sins
A devil has many doors and ways to approach a man and attract him to commit sins. The most known door that a devil creeps through into a man’s heart is the door of humiliating sins and belittling them after he felt despair of letting a man commit great sins. So, he tries hard to let a man commit small sins. A man may also insist on doing small sins because he considers them small ones. But if a man knows how dangerous these sins are on him, he wouldn’t commit them or insist on doing them. It was narrated that the prophet Mohammad (pbuh) says:” Don’t look at the littleness of a sin, but look at whom you dare”. 
Al Imam Al Sadeq (a.s):” Be cautious of belittling sins because they are not forgiven” so I asked (the narrator): what are belittling sins? Al Imam answered:” When a man commits a sin and says: good fortune, I have no other sin”.  It was also narrated that Al Imam Al Baqer (a.s) says:” Be cautious of belittling sins because God will ask you about them”. 
It was narrated that the prophet Mohammad (pbuh) says in his commandment to Abu Zarr:” O Aba Zarr, a man makes a good deed and depends on it, and commits a belittling sin until he meets God angry at him. A man who makes a sin then leaves it will meet God with serenity on the Day of Judgment". 
Belittling sins are sins that a man sees little, humiliates and says (as mentioned in some stories):” I commit a sin then repent. But God almighty says:” We write down what they have sent (deeds) before and their footprints, and We have recorded everything in a clear writing.”. 
Then he who humiliates a sin and belittles it, doesn’t he know that however the sin is small or worthless, is considered great because he’s disobeying God the greatest? Then, a believer shouldn’t humiliate any sin because this sin may not be forgiven because of humiliating it and belittling it.
A small sin may be accompanied by the absence of modesty and fear from God almighty and indifference. This is the reason for not forgiving this sin. Therefore, this small sin will be transformed into a great one, as stories mentioned. 
Guidance and Good Tidings, Al Maaref Islamic and Cultural Institution
 Al Sheikh Al Kulayni, Al Kafi, part 2, page 27
 The master Mohammed Saleh Al Mazandrani, Explanation of Usul Al Kafi, part 9, 0244, Comments: Mirza Abu Al Hassan Al-Shaarani / Adjust and correct: Mr. Ali Ashour, Dar Revival of the Arab Heritage of Printing, Publishing and Distribution - Beirut - Lebanon, Dar Reviving Arab Heritage For printing, publishing and distribution, first edition, 1421H- 2000.
 Review: The Economic that leads to the path of guidance, oage 144, freely.
 Those who agree in this opinion: Al Sheikh Al Mufed, Ibn Al Baraj Al Turabulsi, Abu Salah Al Halabi, Ibn Idriss Al Huliy, Al Sheikh Al Tusu. The latest relates his explanation in Majma’ Al Bayan totally to our friends.
 Al Allama Al Majlisi, Bihar Al Anwar, part 74, page 168.
 Al Sheikh Al Kulayni, Al Kafi, part 2, page 287.
 Same source page 270
 Al Allama Al Majlisi, Bihar Al Anwar, part 74, page 79.
 Surah Yassin, verse 12
 As will be mentioned in the coning lessons.