\define[2]\epigraph

  {\blank

   \startframedtext[middle][frame=off,offset=none,width=fit,align=middle]%

   \color[darkgreen]{#2}\endgraf

   \rightaligned{\it #1}%

   \stopframedtext

   \blank}

I want to do something like:
\epigraph{Elbert Hubbard}{
Many people fail in life, not for lack of ability or brains or even
courage,

but simply because they have never organized their energies around a
goal.}

Because I want to have the but on the second line, with the rest of the text. But this gives:
Runaway argument?

With the definition of \define in MkII the argument of the command can’t contain a paragraph, a workaround is to define the \epigraph macro with

\long\def\epigraph#1#2{...}

or to use MkIV.