On 6 November 1919, at the joint meeting of the Royal Society of London and the Royal Astronomical Society, the results of the two British expeditions, which observed the total solar eclipse of 29 May 1919 in Sobral, Brazil and in the island of Príncipe, then part of the Portuguese colonial empire, were announced. The four British expeditioners—astronomers A.S. Eddington, C.R. Davidson, A.C.C. Crommelin, and clock mechanisms’ expert E.T. Cottingham—observed the background of stars behind the sun, and following a hard work of data analysis confirmed the light bending prediction by Albert Einstein, put forward by the then recent general relativity theory (1915–16). During the 1910s the theory of general relativity was far from being a fully-fledged scientific theory, Einstein’s capital of credit was still on the rise, and most astronomers’ knowledge of physics was deficient. By dislocating the historical gaze from the British expeditions as a vantage point to read the historical record backwards, in this chapter we start instead from the preceding expeditions to address various questions: How does one explain astronomers’ interest in testing light bending, under very taxing, if not outright dangerous, conditions? Why and how do cognitive flows, which have not yet become accepted knowledge, transgress disciplinary boundaries, and turn into successful predictions? How can we explain the importance of cognitive flows across disciplines in face of successive setbacks? Is it because experts of all types really look after successful predictions? Does success/failure need qualifications, and if yes, under what circumstances?