Well...

What if we have to choose between 1 unjustified death and 10 unjustified deaths?

(I am broadly sympathetic. Some people think that 'moral dilemmas' are moral dilemmas because whatever you do it is morally wrong. For example, if you allow 1 unjustified death then that is wrong. If you allow 10 unjustified deaths then that is also wrong. So no matter what you do (in that situation) you do do wrong.

Other people think that the right thing to do is the best thing to do GIVEN THE CIRCUMSTANCES, however. They might say that it would be right to allow 1 unjustified death GIVEN THE CIRCUMSTANCES in which you must decide between 1 unjustified death and 10 unjustified deaths. Whereas allowing 1 unjustified death GIVEN THE CIRCUMSTANCES in which it is preventable would of course be wrong. So... right and wrong is relativized to the available options and what is right and what is wrong can vary as the available options vary).

What is the difference between these two above ways of putting things?

One difference would be... Whether you should beat yourself up for having done wrong... Or whether you should console yourself for having done the best thing that was available to you given the circumstances...