No wonder most of us give up on our 'get fit' regimes when we continuously punish ourselves when exercising - it is difficult to motivate yourself that way. You have experts telling us how difficult it is to stay in shape. No excuses though! Just work harder!
We punish ourselves for not working hard enough, we are penalised for not achieving artificial targets, feel inadequate for not "getting it".
Instead, let's recapture the enjoyment for movement that we had as children. It doesn't mean however that it has to be non-challenging or mindless: have you seen how much effort and focus kids can put into playing?