Her cat was diagnosed with diabetes many years ago. She never did a single blood test at home. Eventually, she moved him over to Hill's diabetic cat kibble and took him off insulin. He lived for quite a few years after that and his death didn't appear to have anything to do with the diabetes (I don't actually remember the cause of death but he was 19 so he wasn't exactly a baby). Needless to say, I recognize that this was probably just good luck on her part (or on Kitty's) but she feels differently.
This is what's called antecdotal. There are always stories where someone was lax with treatment and survived a disease just fine.
But then you have someone like me who saw firsthand a cat pass out and nearly die from low blood sugar by being dosed blindly with insulin several times, and the cat died prematurely after the blood sugar became hard to manage due to poor treatment in the first place.
So taking antecdotal evidence from one source is just bad news. Scientific research and antecdotal accounts from MANY sources show that testing is necessary to manage diabetes in most cases and it can be dangerous to blind dose insulin. So there you go.
There are diabetic people for that matter that manage their diabetes poorly and don't always test, and live to a ripe old age, but you don't see doctors recommending others do this because some people did fine being irresponsible with their treatment.
Not all diabetics have the same blood sugar numbers, nor does their blood sugar respond the same to insulin dosing, or respond the same to the same amounts of insulin. The body just doesn't work that way, and we're talking about an organ (the pancreas) which is producing insulin at erratic levels, which will vary from diabetic to diabetic.
One diabetic may have high blood sugar that stays pretty consistent, so blind dosing works just fine for them, even if not recommended. Other diabetics may have blood sugar that goes all over the place, and while blind dosing insulin worked one day, the next day it caused them to become hypoglycemic. You just CAN'T blind dose and assume you will have good results.
Then there's the fact that after treatment is started the pancreas will often respond by pumping out different levels than it was previously. So while dosing with a certain amount of insulin worked for a long time, suddenly you have a hypoglycemia situation.