'If we persistently devote ourselves to God and keep a careful watch on the soul's passible aspect, we are no longer driven headlong by the provocations of our thoughts. On the contrary, as we acquire a more exact understanding of their causes and cut them off, we become more discerning. In this way the following words come to apply to us: 'My eye also sees my enemies, and my ear shall hear the wicked that rise up against me.' (Ps. 92:11. LXX)
St. Maximos the Confessor
The whole purpose of the monk's warfare against demons is to separate the passions from conceptual images. Otherwise he will not be able to look on things dispassionately.
St. Maximos the Confessor
Well, one can go on and on and on.. there are so many ways they can act upon us.. it is hard to say more concisely than simply.. 'Keep watch!' Watch and see, see how one is suddenly desiring more than one naturally should.. see how it happens at a particular time and place, disposed to do you harm.. see how it affects your life in general to keep you enslaved to 'the world, the flesh, and the devil' and to prevent you from doing good.. 'Keep watch!'
Dispassion is amongst other things, key towards being able to judge and evaluate the real virtue or lack thereof of our everyday actions and lives. If we feel pleasure about something that is sinful, and judge it morally good -- but it is not, well, that is the path of destruction. And moreover, generally, enslavement to the sin because of how we feel about it. The demons will seek to reinforce this attachment and keep us 'slaves' to 'the world, the flesh, and the devil.'
I could post a whole series of quotes on the various aspects of the matter.. but that's not a concise answer it depends on what exactly one wants in the answer.
Sin as it is said, puts people under the domain of the devil. We start off in fact, in that domain and under a certain authority thereof by default because of Adam and Eve.