你以为轻易地就能打败他，那你就大错特错了。

If you think you can easily beat him, you're all wet.

《新英汉大辞典》

从未怀疑过你的信仰，那你就大错特错了。

If you never doubt your beliefs, then you're wrong a lot.

youdao

如果你相信新闻报道已经与人们的生活没有关系，你就大错特错了。

If you believe that news reports have no connections with people's lives, you could not be more wrong.

youdao

It's wrong to think that you feel weightless because you escaped the pull of gravity.

但是要是你认为失重,就是不受重力那就大错特错了

耶鲁公开课 - 基础物理课程节选