I suspect more people at some point have had the position where they've got home and found there was something where they didn't pay for it.
In my case I'd picked up two cards that were stuck back to back.
That happens.
But then you have a choice. In my case, I took the extra card back, handed it in and explained what had happened. End of story.
Now I wouldn't necessarily have blamed you the first time if you'd just thought "oh well" and kept it. A fair number of people wouldn't have even noticed, and it was an accident.
But to continue doing it is really wrong.
As others have said, don't use the self scanner. Perhaps limit yourself to going in the shop less often. And also realise (we have police radio at work) that they may be perfectly aware you are doing it, and are waiting for the right moment to pounce.
We get "call 99" calls where we can hear the security alerting the police, and making a decision whether they will catch the person this time or next. You will be on CCTV, and they may well be saving evidence.
Once you've been caught you may find that you are banned from the shop. Also, as again I know from police radio, when you're in town, other local shops may be put on alert that a known shoplifter has just entered, and they may decide to escort you out. Sainsbury's certainly has a few people who are asked to leave upon entry due to dodgy dealings on self-checkouts. One of them gets very mouthy, so they often ask for support.
I do think getting people to listen to how much known shoplifters are watched by the police/shop security and CCTV would put a number off.
There are times when it really is a case of:
"Calling 99: Boots calling Known shoplifter, escorting out. Can you check CCTV. About 5'6, black hair, blue coat and a buggy. They're heading towards Primark."
"Primark here, can see them."
"Leaving Primark going west towards Sports Direct"
"Sports Direct here, getting security on door..."
"99 here, clear evidence of them taking items at Boots and Primark, sending officers down."
10 minutes later. "Calling Boots, Primark. Person remanded. Can you come and identify your property?"
No it isn't always as simple as that, but it does happen.