原因是如果没有正确的指导，钢琴家必须通过反复实验和不断犯错来探索正确的运作方式等技巧。

The reason is that, without proper instruction, the pianist must discover the correct motions, etc. , by trial and error.

youdao

反复项目能让您在每个反复项目完成时示范可部分运作的产品，并依据示范时得到的意见采取动作。

Iterations let you demonstrate a partly working product at the end of each iteration and act on feedback from that demonstration.

youdao