Halo friends (and other).

I am not in bonsai a long time but one thing takes my wondering.
When look clips on Youtube, some really good masters cut the roots and branches of for 3/4. It seams unbelievable. How that can not work for me and work for them? What could be the reason?

Timing, knowing the species, and not at random cutting. And aftercare.

You do not need to be a master to do this.

Split wrote: When look clips on Youtube, some really good masters cut the roots and branches of for 3/4. It seams unbelievable. How that can not work for me and work for them? What could be the reason?

Most of the time these procedures are done at the wrong time by beginners.
If done at the right moment, and taking good care, it can be done in most of the species used for bonsai.
Don't try it on a Leptorspermum Scoparium (NZ Teatree) though, it will die.
But maples and some pines are famous for surviving very severe root pruning.