Some Varieties of Failures of Agency
A. Paul Holmer on Weakness of Will (or lack of desire)
… when I can no longer decide between opposing options, or when I completely lack wants and wishes, then much of daily life loses its challenge, and I begin to think there is little sense left. The philosopher Aristotle noted long ago that many persons suffer from a weakness of the will.
But a tragedy is in the making when a person does not learn what every person finally must learn: that is, some powerful and persistent wants. For unlike the animals whose wants are given with their very birth and nature, persons have to spend time learning what their proper wants are. And if one does not want what is essential and needful – for example, to be morally sound, to be intelligent and informed rather than stupid, or even to be healthy rather than sick – then a good part of being a person is missing. 
If a person is always restless and anxious, there can be no resoluteness of will. With little or no will, there is nothing clear or definitive about such a person. Sometimes it is hard to know whether the lack of volition comes first and the restless anxiety follows, or the reverse. However, we need not decide such questions in order to say that surely the two go together. A sign of being weak-willed is to shift from one thing to another. Having a will for this, then for that, in endless succession, is really to have no conclusiveness and no character at all. Such a mode of life spells chaos after a while. Soon one does not know what will satisfy, and a lifetime can be spent in meaningless pursuits. … Something like this happens to us when we spend ourselves in preoccupation with pleasure. [86-87]
from Making Christian Sense (The Westminster Press, 1984).
B. Oliver O’Donovan on Indecision
The peculiar moral weakness we call “indecision” is not a weakness of love; it cannot be countered by a relentless ratcheting up of the affections. It is a weakness in discerning and hearing a call to act, a weakness in observing a practical possibility given in the shape of the moment, and that is a weakness of hope, for hope discerns in the light of God’s promise what is given to us to do. Where love attends to the “today” that has come to be out of the past, the “today” of the world around us, hope attends to the “today” that has not yet come to be, but opens out in front of us, the “today” of opportunity. Hope presides over the venture of action and focuses deliberation on its possibility.
from “Sanctification and Ethics,” in Sanctification: Explorations in Theology and Practice, edited by Kelly Kapic, (IVP Academic, 2014), 159.
C. Daniel A. Westberg on Inaction
1. Distraction from purpose
[There are] cases where there is a lack of harmony between the judgments of our practical reasoning and the actual things that we do. … [For instance,] we may simply not “feel like” doing something. The laundry is postponed in favor of reading a magazine; we omit the exercise that we had decided to do; we eat more at dinner than we had originally planned; we curtail or omit our prayer time. We do not get around to writing the letter that we had planned, and we find that we had spent unplanned time on video games, or internet surfing or a number of other things not wrong in themselves but that in reference to our plans and prior decisions amount to a deflection from our aims. This is part of the human condition, of course, and part of the material for our reflection that “we have left undone those things which we ought to have done.” 
If you do not carry out in action your brilliant insights and decisions, you lack the virtue of prudence. … Your good intentions, your “to-do lists” and plans for the future, are all very good (and may exhibit a certain insight, practicality and wisdom), but if they are not translated into actions, there is no true virtue of practical wisdom in action/actuality. 
3. Lack of initiative
Aristotle included in his understanding of courage the kind of person with noble ambition, capable of major achievements worthy of respect and honor. … [In Thomas’ treatment] this is the virtue of our great heroes and saints, those like Francis Xavier and Ignatius, John Wesley and the missionaries Hudson Taylor and Adoniram Judson, those who achieved something on a grand scale and inspired many others. … The characteristic of this virtue that makes it part of fortitude is that it has to do with achieving something good and of value on a large scale, and therefore involves challenge and difficulty. It is the ability to pursue a vision successfully in spite of hardship and discouragement that gives Thomistic magnificence, better understood as enterprise or initiative, its place and character as a virtue. [205-6]
from Renewing Moral Theology (IVP Academic, 2015).