Why does DNA fingerprinting work for identifying humans?

In the noncoding regions of DNA, humans have repeating sequences called tandem repeats. The number of these repeats is quite variable and no two humans, unless they are identical twins, have the same repeats. When restriction enzymes chop up DNA, the fragments produced are different sizes because of the variability of tandem repeats. These differences become apparent when DNA digests are separated by size using electrophoresis.