Money

Why is it that when we (husband and I) have money I am like a miser, never wanting to spend a penny. Then when we don't have money I am spending like there is no tomorrow?
You may ask why I bring this up. We are shopping for a riding lawn mower. We need one, this is not a frivolus expense. We have over 2 acres (actually Paul has) to mow, it is hilly and can't be done with a push mower. So why don't I want to spend the money? I would much rather horid the money away in a savings account and forget it is there. I know this is an investment in our home, but I don't wanna!