pull oneself up by one's bootstraps

Etymology:

• Early 19th century US; attested 1834. In original use, often used to refer to pulling oneself over a fence, and implying that someone is attempting or has claimed some ludicrously far-fetched or impossible task. Presumably a variant on a traditional tall tale, as elaborated below. The shift in sense to a possible task appears to have developed in the early 20th century, and the use of the phrase to mean “a ludicrous task” continued into the 1920s.
• Widely attributed to The Surprising Adventures of Baron Munchausen, by Rudolf Erich Raspe, where the eponymous Baron pulls himself out of a swamp by his hair, though not by his bootstraps; misattribution dates to US, 1901. The Adventures is primarily a collection of traditional tall tales; using bootstraps presumably arose as a variant on the same tall tale, or independently.