人是鐵飯是鋼

1. • one can't function properly on an empty stomach (idiom)
2. • an empty sack cannot stand upright

Character by character

• 人(rén)person
• 是(shì)be
• 鐵(tiě)surname Tie
• 飯(fàn)cooked rice
• 是(shì)be
• 鋼(gāng)steel