In what ways does pride, envy, hatred or selfishness break Tawheed? Could you explain what is meant by the sin of Shirk?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. Nothing nullifies Tawheed except something which is proved to be a nullifier of Iman. As for any sin lesser than that such as the things you mentioned in your question, it does not nullify Tawheed. But it weakens it. Such sins can gradually weaken Tawheed until leaving it inexistent. Allah Says (interpretation of meaning): {By no means! But on their hearts is the stain of the (ill) which they do!}[73:14]. Several interpreters of Qur'an think that what is meant in this verse is that sins keep on piling up on the heart until it becomes black. Ibn al-Qayyim said in this respect: The fact that sins weaken Iman (belief) is something known by commonsense and taste. As narrated in the Hadith when the person commits a sin a black mark is engraved onto his heart. If he repents and asks for forgiveness, his heart gets cleaned. But if he returns and commits another sin, another mark is engraved onto his heart until his heart gets covered. This is what Allah Says (interpretation of meaning): {By no means! But on their hearts is the stain of the (ill) which they do!}[73:14]. Bad deeds blacken the heart and extinguish its light while Iman (good faith) is a light in the heart. Bad deeds take this light off or reduce it. Good deeds increase the brightness of this light while bad deeds extinguish this light. Allah mentions that what the hearts accumulate is the reason for this covering up of these hearts. Allah Says that He punished the hypocrites for what they had committed. Allah Says (interpretation of meaning): {…Allah hath upset them for their (evil) deeds….}[4:88]. Allah also Says that the breaking up of the covenant He has taken upon everybody is a cause for the harshness of the hearts. Allah Says (interpretation of meaning): {But because of their breach of their Covenant, we cursed them, and made their hearts grow hard: they change the words from their (right) places and forget a good part of the message that was sent them…}[5:13]. He made the sin of breaching the covenant as a cause of these effects: harshness of hearts, curse, changing the words from their appropriate places and forgetting knowledge. Sins for belief are like illness and fever for body strength. One of the rightly guided predecessors said: Sins are the mail of Kufr as the fever is the mail of death. Ibn Taymiyah said: No doubt that sins can be a cause of Kufr. So one should avoid them lest dragging him to Kufr. Allah Says (interpretation of meaning): {….then let those beware who withstand the Messenger's order, lest some trial befall them, or a grievous Penalty be inflicted on them. }[24:63]. What is meant here is "Kufr/disbelief." From the above you can deduct that envy, pride, selfishness and all other sins weaken the Iman. It is feared that those who keep on committing sins may lose that belief (Iman). For more details, please read: 82456. Allah knows best.