I think one of the simplest ways to illustrate this is with sounds. Humans who spend their early years in an environment devoid of certain sounds lose the ability to differentiate those sounds. The classical example that many seem aware of are Japanese speakers who have trouble distinguishing l and r sounds. Every language has some sounds missing, and so any given person should be able to find two sounds they can't distinguish unless they were raised in a multi-lingual household from birth which covered all the sounds.