Brush modifying changes previous strokes.

Hi Monica,
I don't get it.
Why would anyone want to edit all the previous line thicknesses by default?
One would only choose to do that if all the previous paths are selected.
I haven't even selected them.
I done even want to edit the existing path.
I want a new brush before I draw the stroke, just like when illustrating, so I can see what I am drawing.

I realize vector illustrating is not the same as bitmap programs or traditional, but isn't that cumbersome in the extreme?
I mean, I change brush widths thousands of times.
Why would anyone want to change the whole drawing unless they select it to change

I have also noticed that the brush width on the Properties bar ( or is it 'Control Panel' in Adobe) keeps changing back to 1 point when I say set it at 7 point when I apply the brush to the page.
I usually have to do several demos in the corner of the page before the (say) 7 point

You don't have to answer this last paragraph because it appears a 'given', as arduous as it is.

Thankyou for your help, you are very gracious, and I don't believe I used that button, or it was not active. Maybe have to limit my line drawing to Corel, and then import it into AI, seeing it is supposed to be the "industry requirement" now.