Full Idea
The actions a virtuous agent is forced to in tragic dilemmas fail to be good actions because the doing of them, no matter how unwillingly or involuntarily, mars or ruins a good life.
Gist of Idea
Involuntary actions performed in tragic dilemmas are bad because they mar a good life
Source
Rosalind Hursthouse (On Virtue Ethics [1999], Ch.3)
Book Reference
Hursthouse,Rosalind: 'On Virtue Ethics' [OUP 2001], p.74
A Reaction
Of course, only virtuous people have their lives ruined by such things. For the cold or the wicked it is just water off a duck's back.