A Hard Lesson

Book fairs are exciting times at an elementary school. But they can be frustrating too.
For one reason: the one that comes to our school has decided the only payment method available is by pre-loading a card for each child with some money. They recommend starting with $30. Well, we share that load with the grandparents and each of us contributes a bit to get them up close to that, though we don't always make it. Because wow that's a lot of money for a child to have at once.
Another frustrating part is that you don't know exactly what books are available ahead of time to help your child plan and budget. So, when they visit the book fair with their class, they find a book they want and buy it, not worrying about how much it costs or if they'll have enough left over for something else.

And the last hard part is the lesson every American has to learn eventually. Tax. Yep. Sales tax gets you every time, and when they add in sales tax to your book, your money doesn't go quite as far as you thought it would.
Needless to say, when my 7-year-old spend $14 on a book the first day of the fair, he discovered he couldn't get the other book that looked interesting to him. Because the tax had eaten up what he thought he'd have as a cushion. And if he could handle saving the money to use next year and having that extra money to help buy more books then, it wouldn't be that big of a deal.
But my son has this issue of money burning a literal hole in his pocket. He knows he has more to spend. How can he make it work even though he can't have the other book he really wanted? Is there another book he could settle for?
I tried to explain that settling for a book wasn't nearly as great a choice as saving the money for next time and getting more books he really loves. But he's seven. So it didn't sink in.
He came home with two cheaper books. Has he read either one of them? Not to my knowledge. One, he bought because it had a fake shark tooth on the cover. Need I say more?
Of course, now he won't have a cushion to start off his budget next year. Which means we'll probably go through this all over again. Will he remember the lessons we tried to teach him this year when it came to really thinking about how much to spend on each book so he'd have enough?
Probably not.
But maybe in a few years it will.
Do you have hard lessons you've tried to help a younger person learn only to have them completely ignore you? Or do you have a time when you had to learn a hard lesson and it's stuck with you for the rest of your life? Was it anything to do with books or taxes?