Most of the issues are highly technical. Two or three countries are happy to pool sovereignty and integrate further. But each is fighting its national corner too. Each leader has impassable red lines. The outcome is likely to be a carefully-packaged fudge.
Failure is unthinkable.
Currently 62 votes out of a total of 87 are required to block a proposal. All now have 10 votes. Luxembourg, population 400,000, has two. Spain, a famously tough negotiator, wants more to reflect its medium size. Most states support a double majority voting system where decisions would require both a majority of weighted votes and a majority of the EU's population.