Another metaphor that Ball criticizes is that of a protein with a fixed shape binding to its target being similar to how a key fits into a lock. Many proteins, he points out, have disordered domains — sections whose shape is not fixed, but changes constantly.

I dunno, kinda sounds to me like a good educational metaphor. Yea, not 100% accurate but good enough for high school biology. You need to make some simplifications for the sake of education. Not everyone can care about the complex intricacies of genes and proteins.