Your preaching to the choir here LaQueen, I know, I know.
I told my friend off (in a light hearted way) for the time she made both of us late in leaving a shopping centre to go pick up our kids from nursery.
I stooopidly believed that if she travels in my car, then there was no possible way she could dawdle and waste time as she would be running on my time
But no. Despite repeated text messages, impatient phone calls, beeps on my horn out side the shop, she rolls up to the car at the time when we should bbe in the vicinity of the school. (20 mins minimum away)
My rant to her was about 'taking into consideration'. She honestly believed she could cram her "quick stop" into the Vodafone shop, get what she needed to, pay for it, get out back to the car, get settled into the car all within 10 mins. She was 45 minutes 
She did not take into consideration:
The walk getting from the shop she was in, to the phone shop. (opposite ends of the centre!!!)
A large queue in the store
That an assistant would be available to serve her straight away
Her baby in the pushchair would stay asleep and not wake up and fuss.
Pretty much all these things happened, and my point to her was that if she had thought to herself before hand, "hmm, what if there was a queue. No way could I be served and back in the car within 10 minutes.." then she would have reasoned to forego it for another time.
The icng on the cake was when she told me as she was getting served the till computor froze
. It always happens to her!
And yes, I know I sound sooo bloody sanctimonius 'telling off' my friend , but this happens nearly everytime we make arrangements, and each time I bit my lip and 'low it. It's dawning on me that I'm enabling her, I think.