They're so cool that sometimes they must attack, even when it's a bad idea... I'm thinking of the cinematic intro of dawn of war: marines leaving the cover of ruins to frontally attack the orcs.
And sometimes, the weaker can fight very well. Lobo (aka The Man), after beating some dude, admit with pleasure that it was a good fight.
Rule of cool works both way: the weaker (Terrans) can fight "over the top" when facing stronger enemies (Tyranids).