The expansion of our awareness is only possible through solving those tasks which are matched to the actual status of our training. The tackling of tasks which are «too difficult» does not lead to any kind of acceleration of our development. In fact it is the opposite, it leads to a slowing down or even to a standstill or to steps backwards. The same is also true where the demands are insufficient.
This is immediately obvious in virtually every other form of training: A music student who learns a piece which is too difficult for him during his training will not make faster progress in his learning process than another musician, who only plays pieces which are matched to his actual abilities. If a good piano player only ever plays quite simple pieces with one hand, in time he loses his ability with the second hand: He takes steps backwards or forgets what he has learned about two-handed piano playing. A car driver who also drives a formula one racing car, will not become a better car driver because of this. A sportsman who trains to run over a length of 5 km will obtain no advantage at all for his 5 km stretch by completing a 42 km marathon, even if he finishes the marathon in a very good time.