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The dwarf satellites of `giant' Milky Way (MW)-mass galaxies are our primaryprobes of low-mass dark matter halos. The number and velocities of thesatellite galaxies of the MW and M31 initially puzzled galaxy formationtheorists, but are now reproduced well by many models. Yet, are the MW's andM31's satellites representative? Were galaxy formation models `overfit'? Thesequestions motivate deep searches for satellite galaxies outside the LocalGroup. We present a deep survey of the `classical' satellites($M_{\star}$$\geqslant$4$\times$10$^5 M_{\odot}$) of the MW-mass galaxy M94 outto 150 kpc projected distance. We find $only\ two$ satellites, each with$M_{\star}{\sim}10^6 M_{\odot}$, compared with 6-12 such satellites in the fourother MW-mass systems with comparable data (MW, M31, M81, M101). Using a`standard' prescription for occupying dark matter halos (taken from the fullyhydrodynamical EAGLE simulation) with galaxies, we find that such a sparsesatellite population occurs in $<$0.2% of MW-mass systems $-$ a $<$1%probability among a sample of five (known systems + M94). In order to producean M94-like system more frequently we make satellite galaxy formation much morestochastic than is currently predicted by dramatically increasing the slope andscatter of the stellar mass-halo mass (SMHM) relation. Surprisingly, the SMHMrelation must be altered even for halos masses up to 10$^{11}M_{\odot} -$significantly above the mass scales predicted to have increased scatter fromcurrent hydrodynamical models. The sparse satellite population of this `lonelygiant' thus advocates for an important modification to ideas of how thesatellites around MW-mass galaxies form.

A Lonely Giant: The Sparse Satellite Population of M94 Challenges Galaxy Formation