Comment by pfdietz

Nor can you count on Common Lisp to have TCO. People who are new to CL and treat it like Scheme run into this constantly. Basically never recur down a list, since the list could be long.

This problem also shows up in cases where TCO is not possible. For example, suppose we have a syntax tree for some program and need to traverse the tree. Nodes that represent lists of things might have a long list of children, and in a sufficiently large program recursing down that list can blow out the stack. Just recurse on list elements, which one can reasonably assume don't nest too deeply.