I have been considering taking out my relatively small initial investment (<$10K) so that any gains are just gravy, but I put it in willing to lose and and want to see where this horse rides for 5 years.
If it goes to $0, so be it. If it ever gets to the point that I can pay off my house, that is when I will have a difficult time not pulling it out.
I've been thinking of a reasonable "exit" strategy, and thinking of starting to sell 1-2% of my holdings per month at some point.