JET has provided a test bed over the last ten years for detailed studies of the influence of electromagnetic (EM) and fast ion effects on transport, turbulence and energy confinement. This paper reviews the important synergy between experimental results and high performance computing simulations, which has allowed to unveil the extraordinary role of EM and fast ion effects to reduce or even suppress ion heat transport. These results are essential to understand future DT burning plasmas dominated by fusion born alpha particles.