Parenting Advice: Pay Now or Pay Later

When I was pregnant with my oldest, a married couple who had an adorable one-year-old invited us over for dinner. I glowed with excitement over our pending arrival (the glow mostly produced by sweat and nausea), and listened carefully as these veteran parents filled my head with advice.

After dinner, we sat around the coffee table with a deck of cards while their angel slept. It was early days yet, not even a flutter of movement, but I was happily ensconced in my pending motherhood. They were newly from the trenches of infanthood and felt confident to instill a little of the serious wisdom from the front. 
Some of it horrified us: what sort of parents would liken their precious-darling-miracle-of-life to a goldfish who spends her day staring at them until, finally, she smiles?
Some of it confused us: what was this thing called baby wearing?
One piece of advice they gave us, however, has become a family motto: pay now or pay later.
Trying to get your child to sleep in his or her own room? Pay now with a few sleepless nights or pay later with years of getting out of bed.
Want your children to eat their vegetables? Pay now with cries of disgust or pay later with years of cries of disgust.
Sometimes we pay now and sometimes we pay later. But it still pops in my head when I’m presented with a parenting choice. 
What was the best parenting advice you ever received?