Clive Thompson summarizes this surprising study [PDF] by Davy LeRouge and Luk Warlop on how the better you know your spouse, the more likely you are to buy them crappy gifts they hate.
The result? People were pretty good at predicting the likes and dislikes of total strangers -- yet astonishly crappy at figuring out the preferences of their closest and dearest partners. And when they were given new information about which furniture their partners picked for themselves? It didn't help. They were still better at picking gifts
for total strangers than for their loved ones.
Why? Possibly, the professors theorized, because when we're very familiar with our spouses it can be hard to separate our own preferences from theirs. We mistake things we'd like for things they'd like. Also, we tend to cherish hidebound ideas about what our partners are like, and we're unable to step outside those assumptions -- even when our partners themselves give us fresh, new information. When we face down strangers, we have none of those biases and thus are able to more clearly see them as they are.
I use a similar approach with my kids, but tend to listen less to what they're asking for in the time leading up to a gift-giving event, and more to what their true likes & dislikes are. For my three boys, gift giving is easy; I usually look for something I'd liked to have had at their age, combine it with what I've gleaned from the above tactics, and get a winner most every time.
But my daughter... That's a different story. And a true challenge.