My wife does a lot of garden work. When she set up TouchID in the winter, it worked fine – until the gardening season started. Then it gradually became more unreliable, until it stopped working altogether. Then early last fall, when she went to the police station for a new ID card, their fingerprint reader was unable to read a fingerprint from any finger. She was told that this is not uncommon for people who do garden work, rock climbing, or some other kinds of manual labour. Their fingerprints just wear down enough for the reader not to be able to read them. – But not completely. Burglars beware. ;-)