I think any experienced programmer can tell you that the only thing that stops projects from completing is time. Almost everything is doable (think Turing Machines, all algorithms are programmable, except those that contradict the Halting Problem), it just takes time, and a whole load of it... Time for testing, reading, reverse engineering... heck, if you don't have docs, it's not impossible, you just have to spend the time to figure it out yourself, then you get to the be the first person to document it.
Good luck.
Just don't make the same mistake as
this guy.