A good statement is what the collector tells their friends when the friends ask about the piece on the wall. If the statement requires the collector to re-read it, it's failing its job.
The best ones we've seen across the continent are 60 to 90 words, written in the first person, and grounded in one concrete observation. Not a theory. Not a manifesto. One thing the artist actually saw or wrestled with that the work is a response to.