"Vice" and "Sin" seemed to be used without distinction sometimes. Understanding the simple difference is useful in understanding one's spiritual struggles and successes.
Vice is anything which opposes a virtue, which is a voluntary habit which inclines one to what is good. A vice therefore is a voluntary habit which inclines one to evil. As habits, virtues and vices are not the same as acts from them. One can have a vice, but the sin is an evil act.
Good works are acts of virtue, and sins are acts of vice.
The Force of Habit is a human characteristics. We tend to do things by habit. Directly ourselves, and our habits, is part of overcoming sin. To direct oneself towards what is good is to develop good habits, that is, virtues. Removing and overcoming bad habits, vices, which are opposed to good, is essential to living in the spirit. It is in our choices and efforts that we find merit or sin. If we will to do good, but struggle in overcoming our bad habits, that is a sign of reduced guilt in the individual sins. Bad habits, vices, plague us, they cause us much grief and frustration at times, but we have to understand that we are sick in the spirit as well as in the flesh, and we need to be healed. God is the source of all that is good and all healing. It is by God's grace, and our cooperation with it, that we find eternal joy.
Vices are like spiritual allergic states. In the flesh, an allergy is something one has in reaction to an allergen. A person can be allergic to nuts for instance, making the mere physical contact with nuts or the oils of nuts dangerous. But, a person with such an allergy is not actually physically harmed by the allergy itself. It is only when triggered is it dangerous. Such people take extra care in avoiding whatever could cause dangerous and even lethal reactions. Likewise, a person with a vice, such as one of the most common (and least realized) vice of being prone to gossip and idle speech, is not actually committing a sin, ie, being spiritually harmed, unless one is given, and then takes, the chance to complete the sin.
That is why avoiding and removing all possible sources of temptations of a particular bad habit (of all sorts, but especially vices) is one of the first and most basic steps to overcoming. Removing the ability to complete the sin shows one's will and intent to do good and it prevents the sin from occurring at all in the future. Naturally, it is not always so simple, especially with some vices which are easily activated. Choosing to put oneself in danger is a cooperation with the vice and clearly indicates more guilt. We will look for excuses to retain the temptations, especially if they are common. If the temptations are found in unimportant social events, entertainment (especially movies), online browsing habits, etc, we will find reasons to retain the acts because the acts may be "normal" and not harmful in themselves. But remember, nuts are not harmful either in themselves, but they can kill those who are allergic to them. The defect is not in the object, but in oneself.
And then there are many times were we cannot avoid the temptations completely. This is especially true of those which mainly originate in one's own passions or in social situations and one cannot withdraw from the world completely (a rare vocation). In these times, one must be vigilant and extra prayerful. One is in "enemy territory" and we do not know what will happen. This is brought to light in the Lord's Prayer. "Lead us not into temptation, but deliver us from evil.". God has pleaded for us to pray for protection against temptation, because God knows the dangers we will face if we rely on our own selves.
One last point is that removing the possibility of completely the vice does not result in much gain. A person who avoids nuts is still allergic to them (as far as I know). A person who removes the ability to complete a sin still has the vice. It is by replacing it with a good habit, with the corresponding virtue, that one grows in holiness. Prayer is especially essential for this because even though we can (to a degree) avoid the sin, we need God's grace to fill us. Any person who is unable to commit a particular sin is not necessarily holy. Even a person who desires to complete the sin would be unable to do so in such situations. It is by growing in virtue that we grow closer to God.
We are human; we have vices. What are they? The most harm comes from vices we fail to recognize in ourselves.