"complete themselves" is a grammatically correct and usable phrase in written English.
You can use it when you want to indicate that something has been accomplished without any outside help or assistance. For example: "The group was able to complete the project successfully; they had the resources and the motivation to complete themselves."
Aravena's "half-houses" are exactly that – houses that leave one side for residents to complete themselves.
His gestures are taut and constricted; they never quite complete themselves.
Along the way they enter some gorgeous paintings come to life and learn they have the power to complete themselves.
The spiraling ramps and circular roof complete themselves in the mirrored reflections; there is not much to the work beyond that.
The historical event of the interviews, as Morgan sees it, brings together "two lonely, disconnected men clamoring for the limelight to complete themselves somehow"; the encounter raises powerful psychological undercurrents.
With a few exceptions — such as some van Gogh-inspired painterly thunderstorms that he made in the late nineteen-fifties, and which I wish he had built on — they are illustrational: tissues of fiction, or caricature, that complete themselves in literary imagination.
After these transformation scenes had completed themselves, "Cries of Beverley! echoed instinctively though the house".
Once inside we followed our moods, webpages listlessly completing themselves in descending strips, producing all manner of suspense as the news story or piece of erotica toppled slowly into being".
With luck that means this dog will never see the light of day, but bad movies have a way of completing themselves in spite of all odds.
Well, 8.3% of all 2001 returns that taxpayers completed themselves, and 5.2% of those prepared by tax pros, had mistakes connected with the rebates, the General Accounting Office found.
Mr. Sacerdote found that the adoptees in the latter group were 16 percentage points more likely to complete college themselves.
