Me.
A lot has and continues to go wrong, but mostly self-repairing. At some point some failure will be unrecoverable, but hopefully that's a long time in the future.
An even better answer might be my cats. The small number of repairs that need professional assistance are cheaper than the same issues would be for myself. However I don't expect them to last as long, unfortunately. Even though I got them very nearly brand new a few years ago.
I believe the reason that the wick degrades at 'just the right rate' is that the flame actually keeps oxygen from reaching the wick (so it can't itself burn) until the level of wax goes down enough that the top of the wick pokes out of the now lower flame.