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Galactic outflows driven by stellar feedback are crucial for explaining theinefficiency of star formation in galaxies. Although strong feedback canpromote the formation of galactic discs by limiting star formation at earlytimes and removing low angular momentum gas, it is not understood how the samefeedback can result in diverse objects such as elliptical galaxies or razorthin spiral galaxies. We investigate this problem using cosmological zoom-insimulations of two galaxies forming within $10^{12}~\mathrm{M_\odot}$ haloswith almost identical mass accretion histories and halo spin parameters.However, the two resulting galaxies end up with very different bulge-to-discratios at $z = 0$. At $z>1.5$, the two galaxies feature a surface density ofstar formation $\Sigma_{\rm SFR}\simeq 10~\mathrm{M_\odot}~{\rm yr}^{-1}~{\rmkpc}^{-2}$, leading to strong outflows. After the last starburst episode, bothgalaxies feature a dramatic gaseous disc growth from 1~kpc to 5~kpc during1~Gyr, a decisive event we dub "the Grand Twirl". After this event, theevolutionary tracks diverge strongly, with one galaxy ending up as abulge-dominated galaxy, whereas the other ends up as a disc-dominated galaxy.The origins of this dichotomy are the angular momentum of the accreted gas, andwhether it adds constructively to the initial disc angular momentum. Thebuild-up of this extended disc leads to a rapid lowering of $\Sigma_{\rm SFR}$by over two orders of magnitude with $\Sigma_{\rm SFR} \lesssim0.1~\mathrm{M_\odot}~{\rm yr}^{-1}~{\rm kpc}^{-2}$, in remarkable agreementwith what is derived from Milky Way stellar populations. As a consequence,supernovae explosions are spread out and cannot launch galactic outflowsanymore, allowing for the persistence of a thin, gently star forming, extendeddisc.

Rapid Filamentary Accretion as the Origin of Extended Thin Discs