According to the Quran, Nafs (meaning “self”) has some levels; the lowest level of that is called Nafs al-Ammarah which is what orders man to carry out sins. Following this Nafs amounts to succumbing to extremist demands.
Nafs al-Ammarah can cause various moral and social problems and even physical and mental illnesses, making man lose the right path and set foot on the path of ignorance and sin.
Therefore, Nafs al-Ammarah refers to any action or convert/overt behavior which is against the will of God Almighty. Allah wants man to reach perfection and His will is focused on this target. If our desires are not in line with that of God, we end up in following Nafs al-Ammarah.
This is why the Holy Quran recommends people to stay away from those people who only follow their Nafs. “Do not obey those whom We have caused to neglect Us and instead follow their own desires beyond all limits.” (Surah Al-Kahf, verse 28)
Failing to remember God, forgetting His mercies, rule, and authority, following Satan, and implementing extremist actions are examples where Nafs al-Ammarah can lead us to.
God has promised great reward for those who have managed to contain this Nafs. “However, those who had feared their Lord and restrained their souls from acting according to its desires. Paradise will be the dwelling.” (Surah Al-Nazi'at, verses 40-41)