Comment by staunton

It's always a question of what precision you want.

For really any physical system, when describing it at ever greater precision, more and more effects become relevant until you can't calculate it anymore (or even your theory itself breaks down). In this case, the precision they need is extremely high so this is a problem.

For the vast majority of systems, there's no point in going there because the precision of experiments is too low (which means that the experiments feature even more poorly controlled effects which would be unreasonable to model).