Well each section is broke down to exact everything.
Basics are viscosity, too low and it loses film strength, and won't be good underload. And TBN total base number is is the active. Additives and their ability to fight wear and absorb dirt. The max lowest you really wanna go is a 1.0. Prefer no lower than a 2.0.
And obviously oils with a higher TBN to start will typically last longer. But the loss of aTbn is not perfectly linear. It can fluctuate.