A Hatful of Cards Trick

You will need:

A pack of cards.
A top hat. If you don't have a top hat, find a friendly Victorian gentleman and ask if you can borrow his. If that doesn't work, try an inferior sort of hat or - at a pinch - a cardboard box or saucepan. Just so long as the opening is fairly close to the ground, and about 15-20 cm wide.

What to do:

Try to drop the cards from approximately waist height into the hat. Go on, have a go.
No luck? Try challenging somebody else to do it.
They're not managing, either, eh? Shame. OK, skip ahead to the explanation, then come back here and offer them some sort of bet. Maybe they'll tidy your bedroom if you can drop five cards in a row into the hat?
Then proceed to drop every card, one after the other, into the hat. Which you can do, now you know the knack.
Hurrah! You've won the bet, showed the blighter who's boss, and generally saved the day. Time for a swift round of croquet before listening to pater's tales of his expedition to discover the source of the Thames, then hot milk and early to bed, all the better for more adventures tomorrow! Hurrah!

What's going on:

Pretty much everybody will try to aim the cards, dropping them vertically. Unfortunately they'll tumble furiously, and only the very occasional card will hit the hat. They tumble because they fall quickly, and the flow of air around them becomes turbulent, buffeting them around.

The trick is to drop the cards so they fall slowly. Hold them flat, by the edges, and let them gently parachute down into the hat. One or two might miss, but with a little practice it can be remarkably reliable.

When they're falling flat, the cards present a larger face to the air. Hence, they fall more slowly, and slip smoothly through the air. They'll still start to tumble if they pick up too much speed, however - it's worth testing your cards first to spot how high a drop is required for that to happen.