Why don't quantum effects happen in objects larger than a few thousand atoms?

1. Take a glass
2. Fill it with water
3. Hold it
4. Behold the quantum effect

Yes, really. The reason you can see your fingerprints from the inside – despite the total reflection at the glass-air-interface (which is making it look like a mirror) – is the tunnel effect, which is a quantum effect.

The photons can’t really avoid being reflected on the inside just because there is something on the outside – since they aren’t really leaving the glass medium – but they do anyway and go straight through and back.

Here is a picture of it:

More can be read about this phenomenon on Wikipedia (of course).