The fruits of the Holy Ghost are not habits, permanent qualities, but acts. They cannot, therefore, be confounded with the virtues and the gifts, from which they are distinguished as the effect is from its cause, or the stream from its source.
The charity, patience, mildness, etc., of which the Apostle speaks in this passage, are not then the virtues themselves, but rather their acts or operations; for, however perfect the virtues may be, they cannot be considered as the ultimate effects of grace, being themselves intended, inasmuch as they are active principles, to produce something else, i.e. their acts.
Further, in order that these acts may fully justify their metaphorical name of fruits, they must belong to that class which are performed with ease and pleasure; in other words, the difficulty involved in performing them must disappear in presence of the delight and satisfaction resulting from the good accomplished.
So, this is interesting. If one is patient and mild, for instance, and it is easy to be so, and one finds delight and satisfaction in that patience and mildness, then one has these fruits of the Holy Spirit. I guess that would mean that the virtues are therefore perfected.
In other words, when one practices, acts according to, the virtue of patience with ease and pleasure, one has the fruit of that virtue.
I guess then, when it is still difficult, one does not have a perfect or fully-formed habit of virtue.