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The counter-condition to Infallibility is:

That's not a "counter-condition". Try quoting the whole paragraph.

For the Holy Spirit was promised to the successors of Peter not so that they might, by his revelation, make known some new doctrine, but that, by his assistance, they might religiously guard and faithfully expound the revelation or deposit of faith transmitted by the apostles. Indeed, their apostolic teaching was embraced by all the venerable fathers and reverenced and followed by all the holy orthodox doctors, for they knew very well that this See of St. Peter always remains unblemished by any error, in accordance with the divine promise of our Lord and Savior to the prince of his disciples: "I have prayed for you that your faith may not fail; and when you have turned again, strengthen your brethren."

Liturgy is not Infallible for two reasons:

The rite for the celebration of the Roman Liturgy is a precept of general importance, and therefore laws promulgated for the regulation of the rites are infallible. Cardinal Journet says (footnotes omitted, excepting 814):

The great precepts of the canonical power are not only guaranteed by an absolute infallibility in their principle, their foundation, their root; they are also (and this is a result) guaranteed by a prudential infallibility in themselves, directly and formally. It is not enough to say that they can never prescribe anything contrary to the natural law and the law of the Gospel, it must further be held that all are wise, prudent and beneficial. There are "grave and just reasons", said the Council of Trent, that have led the Church to ratify the custom of communicating the faithful under one kind; the same Council declares it "opportune, praiseworthy, pious and religious" to carry the Eucharist in procession; it teaches not only that the Canon of the Mass is free from all error, but also that "it contains nothing but what breathes holiness and piety and lifts up the heart to God"; it affirms that the liturgical ceremonies accompanying the celebration of Mass are well adapted to bring out the majesty of the sacrifice and to facilitate contemplation of the sublime realities it contains. Precepts so universally and constantly proposed cannot lack wisdom, prudence and expediency. John of St. Thomas spoke his true mind on the subject when he wrote that "as for the laws proposed to the whole Church, such as those drawn up by a General Council or incorporated in the Corpus Juris, granting the general approbation they enjoy, it is difficult to admit that they contain even prudential error, so that they are not to be waived without some special permission."[814] Thus, between the absolute assistance of the revealed precepts, and the fallible prudential assistance of particular precepts, one admits a prudential and infallible assistance for each of the precepts of general interest. These can never be imprudent nor even useless.
However, it does not necessarily follow that precepts of general application will always be the most prudent possible. ...
I have mentioned several of these measures of general interest. It must be insisted that they always arise as consequences or determinations of the great ordinances of Scripture. The laws of fasting and abstinence for example are bound up with the Gospel precept to do penance (Matt. xi. 21). The laws prescribing Sunday attendance at Mass, or again, the mode of celebrating Mass, the use of unleavened bread in the Western Church, are bound up with the commandment to commemorate the sacrifice of Holy Thursday (1 Cor. xi. 24).
814 II-II, qq. 1-7; disp. 3, a. 3, no. 5; vol. VII, p. 311: As I have said, most theologians after Melchior Cano content themselves with expressly distinguishing on the one hand all that concerns the substance, the morality and the rectitude of laws proposed to the whole Church, which cannot, without heresy, be said to contain anything contrary to the evangelical or natural law; and, on the other hand, all that concerns the concrete application of these laws, their adaptation to the circumstances, their strictness, their sanctions, and so forth, in which error is always possible. cf. Suarez, De Fide, disp. 5, sect. 8, no. 7; John of St. Thomas, loc. cit., etc. Between these two extreme groups, the first of which contains the revealed and absolutely infallible precepts which cannot be denied without heresy, and the second the particular and fallible precepts, we must, I believe, find a place for canonical precepts of general applicability which are prudentially infallible. For we have seen St. Thomas (in Quodlibet IX, art. 16) recognize three kinds of decisions of the Church: those concerning faith, in which the Church is certainly infallible; those concerning particular facts in which she is fallible; and those that are intermediary, in which piety inclines to take the Church for infallible. There are other theologians who speak, at least in actu exercito, of intermediate decisions. St. Antoninus for example, following John of Naples, distinguishes decisions of the Pope on the particular concerns of private persons—just distribution of offices and benefices, judicial sentences etc.—in which the Pope can err through ignorance or passion; and decisions concerning the good of the whole Church, bearing either on matters of faith or of morals: constitutions, decrees, decretals, in which, if left to her own resources the Church might err, but in which she is in fact protected by the power of Christ (Summa Sacrae Theologiae, Juris Pontificii et Caesarii, III pars., tit. xii, cap. v III, 2). It looks as though there were only two groups here. Really there are three. For the decrees and decretals which St. Antoninus has separated from particular decisions, cannot, for all that, be included along with decisions concerning the faith. The text of John of St. Thomas, cited above, is very clear. Billuart, who does not seem to have seen it, is nevertheless of the same opinion: "After Suarez and Banez, John of St. Thomas adds that the Church can err as regards the circumstances, application and execution of the law, for example by issuing too many precepts and censures, and applying them too strictly. For, he says, all that seems rather to pertain to the prudence and surrounding modalities of the law than to its substance and morality. Cano thinks likewise.... However, when we are concerned with laws laid down for all Christians, it is only out of regard for these very learned men that their reservations are to be entertained: I should not dare to make them mine" (De Regulis Fidei, dissert. 3, a. 5).