Time Travel.

One of those many times when I need it, since I failed to open a window yesterday. 

We think about it lot this time of year, as New Year's Eve approaches.  Through the magic of documentation and "as of" execution, we can often go a little back or forward.  But midnight on 12/31 - that's a tough one.

Only one I know that's tougher, and that's death.  Lots of things can be fixed while the client's alive.  Once he's gone, he's gone.  That Will better be right.