He lives the poetry that he cannot write.
I think it's about the difference between living life and writing about it. There's an idea that poetry expresses something 'more beautiful' than life or reality - so in this quotation, the person doing the living is experiencing the beautifulness of life (but not writing about it), and the 'others' are writing poetry about things they might not ever do. 'Realise' in this sense means 'make real'.
