Are you really getting the bargains you hoped for? This BBC article suggests (maybe) not.
https://www.bbc.co.uk/news/business-59380453
De Sisti beat me to it, I had seen tweets from Which saying that most deals were not deals.
The way to get round it does seem to be what most people in this thread are doing, having an idea of what is wanted, an idea of usual prices and only buying on/near Black Friday if it's a good enough discount to bother with.
I think there's a lot of people who "can't resist a sales board" and think they're getting a bargain and don't stop to think. And it's not just "stupid" people, a dear friend of mine has a PhD in robotics but is also autistic and in a big shop is so 'overloaded' that his maths and common sense brain shuts down and he buys any old shite if it says "bargain". His wife usually tries to keep him out of the supermarket cos it's not worth the bad deals and random shit he brings home for the evening meal despite being given A List.
And of course, that's kinda what shops are now designed to do, override internal sensible decision making and encourage impulsiveness in many ways. It's hard to blame people when there's millions of pounds spent trying to persuade them in many ways including sneaky psychology or distraction etc.
I hate shops, it makes life a lot easier not to buy random shit. I also remember being pretty poor so haven't changed that mentality a lot.