"How can a lame man sell crutches and a blind man light a lamp" is a proverb, which means that people help each other and support each other. "The lame sell crutches": A lame person refers to a person with limited mobility. He needed crutches to walk, but he sold them to others. This shows that he is willing to help people in need. "The blind man lights": The blind man can't see the light, but lights it. This means that although he cannot enjoy the light, he is willing to create some warmth and hope for others. The whole proverb means that even if you have defects or difficulties, you can achieve common progress and happiness by helping others. It emphasizes the importance of mutual support, care and sharing.