But why is it so good to discover our dominant fault? Because in the developing of our inward life, as in business or in a battle, or in a course of study, success follows from skilful ordering, or rationalising, or strategy. In order to build up our spiritual character with success we must plan, we must concentrate our attack. If we try to overcome all our faults at once we shall probably fail; we have to pick out one point and hammer away at that. And, therefore, obviously it should be a strategic point.
But notice, our dominant fault is not necessarily the most serious sin that we fall into. A man may fall once in a way, not as a habit, into serious sin through drink, and yet the fault which he would be well advised to deal with first may be something quite different, say a bad temper. A dominant fault is one which is the root of many others: dig that out and the rest will die too. The faults of which we are speaking are habits. Diamond cut diamond: habits are only cured by habits.
Therefore it is not enough to review our progress once a week or once a fortnight, when preparing for confession. We have to keep the matter more constantly before our minds: we ought to make an examination of conscience every day, and that with particular attention to the dominant habit we are trying to overcome. This self- inspection should be relatively brief; there is a danger in excessive introspection. St Ignatius of Loyola, in a letter to a Portuguese priest, once wrote "If by the grace of God our Lord the soul is at peace with God' (that is, if it is free from mortal sin) 'make the confession short, without entering into details.' So, too, a daily examination of conscience must not be made the occasion of exasperating one's nervous system. We should give more time to asking God for pardon and help, and to strengthening our resolves, than we give to the actual examination of our conscience."
Link (here) to BEFORE THE THRESHOLD Fr. Leonard Boase, S.J.