Oh, life is ambiguity and imprecision. You can't escape it, with diabetes or with anything else.
I mean, nothing we deal with is truly exact. Insulin varies from batch to batch no matter now much they tell you otherwise. Food counts are only averages. 1 stalk of celery = 1 gram of carb? Well, maybe and maybe not; depends on where and how it was grown, when it was harvested, how it was transported and stored, and so on. Generic drugs sometimes are just as potent as name brands and sometimes they're not. Etc. Etc. Etc. Ad infinitum.
We live in a constantly variable world; you have to accept that and deal with it; it's just reality, and reality doesn't care even slightly what we think, it just goes on being reality.
But none of this is a reason to forego opportunities we do have to keep the randomness to a minimum. If anything, it's a reason to do it. As someone once said in another context, life is change and you have no choice about that; the only choice you have is whether you manage change, or it manages you.
Same here. You can't achieve absolute precision; it's out of reach. But when there is something you can do to tilt the odds a bit more in your favor, it's worth doing. IMHO.
And when you've done that, sit back, relax, pet the cat, listen to it purr, and smell the flowers. :)