That would be a fine reason... if you were lifting the box with your hands.

[He arches his eyebrows and regards Ezra with one of his infamous Looks. Qui-Gon is gentle with his admonishment, but the point is made: he won't criticize Ezra for making a mistake, but excuses are not acceptable.]

A mistake when it comes to utilizing the Force can often be attributed to a clouded mind.

Assuming that is the case. If I'm wrong, please feel free to correct me.