remove brackets is Simple?

How can be that this is simple: https://py.checkio.org/ru/mission/remove-brackets/ I spend a week, stop eating and speak to my wife and cannot solve it to pass all extra checks

And this is Moderate - https://py.checkio.org/en/mission/similar-triangles/ ??!! It is just 5 minutes of very simple code?

What is wrong with me or simplicity?