The Baron has it pegged. I just use 1/4 of the OG as my target. Anything more than 1/3 is probably stuck.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk