LetOneGo means that that it is better to complete 9 out of 10 parts of an iteration with deliverable, testable, features, than it is to bring all 10 parts to a level of 95%, with no deliverable, testable features.
One works at the completion of the tenth, making whatever adjustments necessary to bring it to 100% completion.
In success-oriented programming, the celebration of each success brings new energy and experience to the team in the form of discoveries of what it takes to make sure ItWorks. While it may be disappointing to have to LetOneGo so that success can be arrived at on the nine deliveries, it is also true that the success releases resources to concentrate upon the final task.
Other viewpoints
Of course, no account of Success Oriented Programming (SOP) would be complete without comparison to:
I thought FOP was Fear Oriented Programming, which is generally the outcome of ManagementByKickingAss....
BritishCulturalAssumption: LetOneGo means something far more bodily in the UK.