  Our knowledge of stellar evolution is driven by one-dimensional (1D)
simulations. 1D models, however, are severely limited by uncertainties on the
exact behaviour of many multi-dimensional phenomena occurring inside stars,
affecting their structure and evolution. Recent advances in computing resources
have allowed small sections of a star to be reproduced with multi-D
hydrodynamic models, with an unprecedented degree of detail and realism. In
this work, we present a set of 3D simulations of a convective neon-burning
shell in a 20 M$_\odot$ star run for the first time continuously from its early
development through to complete fuel exhaustion, using unaltered input
conditions from a 321D-guided 1D stellar model. These simulations help answer
some open questions in stellar physics. In particular, they show that
convective regions do not grow indefinitely due to entrainment of fresh
material, but fuel consumption prevails over entrainment, so when fuel is
exhausted convection also starts decaying. Our results show convergence between
the multi-D simulations and the new 321D-guided 1D model, concerning the amount
of convective boundary mixing to include in stellar models. The size of the
convective zones in a star strongly affects its structure and evolution, thus
revising their modelling in 1D will have important implications for the life
and fate of stars. This will thus affect theoretical predictions related to
nucleosynthesis, supernova explosions and compact remnants.
