For soft matter to form quasicrystals an important ingredient is to have two characteristic lengthscales in the interparticle interactions. To be more precise, for stable quasicrystals, periodic modulations of the local density distribution with two particular wavenumbers should be favored, and the ratio of these wavenumbers should be close to certain special values. So, for simple models, the answer to the title question is that only these two ingredients are needed. However, for more realistic models, where in principle all wavenumbers can be involved, other wavenumbers are also important, specifically those of the second and higher reciprocal lattice vectors. We identify features in the particle pair interaction potentials which can suppress or encourage density modes with wavenumbers associated with one of the regular crystalline orderings that compete with quasicrystals, enabling either the enhancement or suppression of quasicrystals in a generic class of systems.Matter does not normally self-organise into quasicrystals (QCs). Regular crystalline packings are much more common in nature and some specific ingredients are required for QC formation, which is why the first QCs were not identified until 1982, in certain metallic alloys [1]. Subsequently, the seminal work in Refs. [2,3] showed that normally a crucial element in QC formation, at least in soft matter, is the presence of two prominent wavenumbers in the linear response behavior to periodic modulations of the particle density distribution. This is equivalent to having two prominent peaks in the static structure factor or in the dispersion relation [4,5]. In soft matter systems, the effective interactions between molecules and aggregations of molecules (generically referred to here as particles) can be tuned to exhibit the two specific required lengthscales and thus form QCs. Such systems include block copolymers and dendrimers [6][7][8][9][10][11][12][13][14][15], certain anisotropic particles [16][17][18], nanoparticles [19,20] and mesoporous silica [21].Some of our understanding of how and why QCs can form has come from studies of particle based computer simulation models -see for example [22][23][24][25][26]. Another source of important insights has been continuum theories for the density distribution. The earliest of these consist of generalised Landau-type order-parameter theories [2,3,[27][28][29][30][31][32][33][34]. More recently, classical density functional theory (DFT) [35][36][37] in conjunction with its dynamical extension DDFT [38][39][40] has been utilised. DFT is a statistical mechanical theory for the distribution of the average particle number density that takes as input the particle pair interaction potentials, and so bridges between particle based and Landau-type continuum theory approaches. The DFT results for QC forming systems [4,5,[41][42][43] clearly demonstrate how the crucial pair of prominent wavenumbers are connected to the length and energy scales present in the pair potentials.Whilst the ratio between the two lengthscales...