Unlike Tyrrany or Usurpation, which are vices about a takeover of the resources of your partner, Foolhardiness is a character "vice of excess" that sees us doing the equivalent of "stealing from ourselves" in terms of time, energy, money and everything else psychological. Then of course the partner loses out too. We pick our partner's pocket by picking our own pocket first.
In being unjust as a partner in contributing to achieving a goal, the foolhardy partner is sabotaging their own life's goals - their "mission in life" or "purpose in life" to the direct psychological impoverishment of the other partner. It is unfair and unjust, bold enough to sabotage joint goals by unwittingly sabotaging your own.
People are often being foolhardy, unconsciously, through a lack of Observing Ego, and so when their behavior is pointed out to them, they are offended that what seems a noble effort to them is unappreciated. They use an Immature Ego Defense, called, "Idealization" - which is like "puffing up what you are doing, as if it is actually strategic" when it actually lacks responsibility or understanding of one's own actions, invoking luck or power we don't really have, to save us from our intellectual lack of goal-preparedness. (Learning about the Ego Defenses, you will find them to be a handy, objective measure of a personal character maturity level.)
It is pathologically narcissistic to be foolhardy, of course, given that it produces destructiveness, a "lose/win" instead of "win/lose" behavior - causing a blight of joint resources, all the while pretending (even to one's self) as if they are actually participating in the relationship as a real partner.
The other vice of Heroism as a virtue is called, "Cowardice," where a person succumbs to fear in the way of a goal, ignorantly attempting to define and constantly redefine what is successful (and employing the Defense Mechanism of Denial as their strategy for constantly revising what is defined as "successful" between them.)
Someone who is romantically foolhardy is their own thief, directly countering the goals and dreams of a mate, by robbing them of resources in a deal which only looks on the surface to be successful. It is very close to Naivete, or to too much of a big conscience, mixed with nothing more than dreams.
As a vice which makes partnership within relationships fail to get to goals, and intellectually unattractive, consider foolhardy behavior to be negative in many ways, including in sexual attraction, since it actually depletes the resource reserves of one's partner, even while self-destructing one's own masculinity or femininity through exhaustion of one's resources.