When a doctor announces that his treatment has 75% chance of being effective, what is he doing? Setting expectation based upon past experience/empirical evidence. There is no law involved here, no science (knowing), just personal/professional experience.
Imagine an athlete entering competition with the percent chance of his winning paraded before his eyes, or a couple being married, or an house builder aiming to satisfy his customer.
What does knowing the percent chance of success do for one? Makes one try harder to overcome the odds, or lets one sink into a helpless state of just hoping for the best? Depends upon the individual?
Can the Bible provide any guidance? How about this? "For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would."(Gal.) This reminds us that we are in a warfare with the flesh, that unseen enemy that is not our friend. This enemy can be more or less aggressive, whether for a sick-patient, an athlete, a newly-wed, a builder, etc.
The following powerful declaration from Science and Health will do far more for us than knowing the percentages:
"Rise in the strength of Spirit to resist all that is unlike good. God has made man capable of this, and nothing can vitiate the ability and power divinely bestowed on man." The man referred to here is you and me!