A blind man lights a lamp - in vain. A blind man lights a lamp - to illuminate others. A blind man lights a lamp - in vain.

1. A blind man lights a lamp - in vain: This connection means that a blind man cannot see even if he lights a lamp, so lighting a lamp is meaningless and is similar to a waste of effort.

2. The blind man lights a lamp to illuminate others: This connection means that although the blind man cannot see himself, he can light a lamp to provide illumination for others, which has a sense of selfless dedication.

3. A blind man lights a lamp - in vain: This connection method is similar to "wasting wax", which means that he has done useless work and has no actual effect.