  Despite the nonlinear nature of wall turbulence, there is evidence that the
mechanism underlying the energy transfer from the mean flow to the turbulent
fluctuations can be ascribed to linear processes. One of the most acclaimed
linear instabilities for this energy transfer is the modal growth of
perturbations with respect to the streamwise-averaged flow (or streaks). Here,
we devise a numerical experiment in which the Navier--Stokes equations are
sensibly modified to suppress these modal instabilities. Our results
demonstrate that wall turbulence is sustained with realistic mean and
fluctuating velocities despite the absence of streak instabilities.
