the anal stage of Psychosexual Development
(1-3 Years Old)

The anal cavity and sphincter muscles of the bowel are now the main source of pleasure.  In the earlier expulsion sub-stage, the child has its first encounter with external restrictions on its wish to defecate where and when it pleases, in the form of parents trying to potty train it.  Parental love is no longer unconditional, but now depends on what the child does.  In the later retention sub-stage, parents come to be seen for the first time as authority figures.

‘By producing them [the contents of the bowels] … [the infant] can express his active compliance with his environment, and by withholding them his disobedience.’ Freud 1905