&gt; <i>Why is it an acid test of competence to you? For the theoretical knowledge they imply?</i><p>Because they are so basic.  If you&#x27;ve never heard of a linked list, it means that you&#x27;ve got absolutely no education (formal or self-directed) in programming. (Even looking at the Java docs, you&#x27;d eventually notice the core LinkedList class.)  If you&#x27;ve heard of a linked list but have no idea what it is, it means you&#x27;ve got a terrible education (if formal) or no curiosity (if self-directed).  If you know what a linked list is but can&#x27;t program one, it means you&#x27;re incompetent.<p>I can&#x27;t imagine the existence of a competent dev who can&#x27;t write a linked list class&#x2F;struct&#x2F;whatever.