Its not that dementia makes you screw up; it makes you screw up at the worst possible time, the time when its guaranteed to hurt the worst. This is not just a suspicion or guess; listen to the logic and you will get it.
One key place that got hit by the protein deposits is my frontal cortex or lobe (not sure of correct nomenclature). This is what controls what is called "executive function" or the ability to manage more than one task at a time. I have spoke on this before but this is the key to the whole problem.
Normally to get around in my day, do things and not fuck them all up, I must keep my mind clear from all but what is the main task. I go about my day walking carefully, not tripping over anything or breaking anything through sheer force of focus or thought. Only way it gets done and the second that focus flickers, I trip or things break. Like day follows night.
So I go along all day trying to be productive and not be a cause of problems. And come 16:00 or so in the afternoon, I am tired but happy I did so well today, I had a good long run of almost feeling normal and more importantly, helpful.
Then dinner comes along and I am having such a good day, you know how it is, you feel a special kind of joy or extra bounce to your step when things make you that happy. And that is the scene as you are carrying the plates of food to your family; you are so much into feeling good and normal and helpful and not a piece of shit that you don't see the box in front of you and everything is on the floor, most dishes broken.
One minute you were on top of your personal world, doing great, feeling the best you have felt all day at least and suddenly reality slaps you around like a four year old at Walmart. You sit staring at the carnage, the food you tried so hard not to burn, the plates you made to make your family happy, now all gone and in pieces all over the floor, the dogs doing their part to help.
This build-up to the best part of your day only to be yanked down to the worst it could seem to get is bad enough but kids, this happens just about every freaking day to me. Its like you screw up the most when you want to NOT fuck up the most.
I know few reading this will actually have dementia so maybe you think that you cannot relate. You can; think about it like this: pretend that in your world, for you, every time you work hard and get a raise at work, you uncontrollably do something stupid and get fired. You can do nothing to stop it and since it always happens right after you got a raise, your mind is on the raise, so taking it away at the moment you love it the most would hurt.
I can describe it no better than this......
I hate it.