Some of us get attached to certain knives for a variety of reasons, so those examples go beyond tool into the realm of treasure. I was thinking of this as I was taking photos of some knives to sell earlier this evening. If you'd asked me a year ago, my "never sell" list would have been quite long. Now, it's limited to knives with sentimental value (usually gifts from family and friends) or something that shows enough honest wear from use that a reasonable selling price would make it unwise to sell.