What qualities should a sculpture possess or exhibit to earn the description ‘successful’?

First, for those who commission the sculpture, it must fully satisfy the brief so that they truly love the work and believe it enriches their lives.

Second, and this holds especially true for work on public display, it should enhance the space in which it’s located and the reputation of the institution or the owner.

And third, it will engage the attention and add to the emotional wellbeing of all who interact with it.