I thought I had gotten along in life pretty well without one, but recently I bought a jackknife to carry and use—as opposed to the ones cluttering my closet shelves. It has become essential. A friend pointed out as I bought it that I couldn’t even open the package it was in unless I had one. In the two weeks that I’ve had it, I have used it a half dozen times every day. I could have lived the rest of my life without having a jackknife handy at all times, but I’m glad I took this life detour.