guī gēn jiū dǐ / zhè cì / shī bài / de / yuán yīn / shì / wǒ men de / zhǔn bèi / bù gòu / chōng fèn

归根究底，这次失败的原因是我们的准备不够充分。

In the final analysis, the reason for this failure is that we were not well prepared.