Objection 1. It seems that daring is not opposed to fortitude. For excess of daring seems to result from presumption of mind. But presumption pertains to pride which is opposed to humility. Therefore daring is opposed to humility rather than to fortitude.
Objection 2. Further, daring does not seem to call for blame, except in so far as it results in harm either to the daring person who puts himself in danger inordinately, or to others whom he attacks with daring, or exposes to danger. But this seemingly pertains to injustice. Therefore daring, as designating a sin, is opposed, not to fortitude but to justice.
Objection 3. Further, fortitude is concerned about fear and daring, as stated above (Question 123, Article 3). Now since timidity is opposed to fortitude in respect of an excess of fear, there is another vice opposed to timidity in respect of a lack of fear. If then, daring is opposed to fortitude, in the point of excessive daring, there will likewise be a vice opposed to it in the point of deficient daring. But there is no such vice. Therefore neither should daring be accounted a vice in opposition to fortitude.
On the contrary, The Philosopher in both the Second and Third Books of Ethics accounts daring to be opposed to fortitude.
I answer that, As stated above (Question 126, Article 2), it belongs to a moral virtue to observe the rational mean in the matter about which it is concerned. Wherefore every vice that denotes lack of moderation in the matter of a moral virtue is opposed to that virtue, as immoderate to moderate. Now daring, in so far as it denotes a vice, implies excess of passion, and this excess goes by the name of daring. Wherefore it is evident that it is opposed to the virtue of fortitude which is concerned about fear and daring, as stated above (Question 122, Article 3).
Reply to Objection 1. Opposition between vice and virtue does not depend chiefly on the cause of the vice but on the vice's very species. Wherefore it is not necessary that daring be opposed to the same virtue as presumption which is its cause.
Reply to Objection 2. Just as the direct opposition of a vice does not depend on its cause, so neither does it depend on its effect. Now the harm done by daring is its effect. Wherefore neither does the opposition of daring depend on this.
Reply to Objection 3. The movement of daring consists in a man taking the offensive against that which is in opposition to him: and nature inclines him to do this except in so far as such inclination is hindered by the fear of receiving harm from that source. Hence the vice which exceeds in daring has no contrary deficiency, save only timidity. Yet daring does not always accompany so great a lack of timidity, for as the Philosopher says (Ethic. iii, 7), "the daring are precipitate and eager to meet danger, yet fail when the danger is present," namely through fear.
Source: Summa Theologica (New Advent)