Then 'it worked'. That's the whole point of credit cards. They're trying to dissociate the buying and the paying such that it's easily possible to 'overbuy' and slip into the credit card hell of perpetually trying to pay it off.
The closer you are to 'living pay check to pay check' the easier it is to get you into this. And I suppose for some people it takes multiple larger purchases to get you into it. Popular culture, TV shows, Twitter nowadays etc. don't help and 'legitimatize' it (everyone's talking about it that way, so everyone must be doing it that way, so it's OK to do it that way).
You might be good at "paying it off at the end of the month". A lot of people easily slip into credit card hell that way, because they _can't_ pay it off at the end of the month, because they didn't realize how much of their credit they should really be using. Credit card says you have $2000? Let's spend $2000. At the end of the month I only have $1500 left in my account? Oh crap!
Personally I pay it off in sort of regular intervals, since it's all right there in my online banking. I've never waited for a "credit card bill", even when they still sent them to me in actual dead tree form.