Functional fixedness is a mental state in which one thinks only of standard/typical uses of objects or typical ways of doing things, and thus is "fixed" on the typical functions to the detriment of creative problem solving. It is a type of mental set, or specific way of looking at a problem, that can cause troubles when items/actions need to be considered in ways that are not typical for them. The "candle" problem is, of course, the famous example of this, but I like some others more relevant to real life. By which I mean, my life. When I travel, I sometimes bring oatmeal packets for conference mornings where I might not have time to get food, and I always forget spoons. So, then I spend the morning trying to drink down oatmeal because, well, no spoon. However, if I looked around and thought about things in a new way, I would realize that I could use coffee stirrers as a makeshift spoon. Or, I could even use my toothbrush, if I really had to!
Also, I win the 100 Things synergy award with this post. I just talked about spoons as part of functional fixedness, but spoons also factor into the famous Spoon test of episodic memory and mental time travel, which I may now choose to encode as a future submission for this list, thereby forming a prospective memory that links back to an earlier 100 Things that was posted. You can all be impressed. If you paid attention in class, the person's name who proposed the Spoon test might be in the tip of your tongue, and if you can engage in past elaborative encoding, you might show recall of Tulving's name. Yes, I can do this all day, brining together topics from the 100 Things list!