freud would say. basically. a fixation occurred during anal stage of development. which is the age most people are potty trained. and they learn about holding things in and letting go blah blah blah
like an oral fixation, only anal?
The Anal Stage
At one and one-half years, the child enters the anal stage. With the advent of toilet training comes the child's obsession with the erogenous zone of the anus and with the retention or expulsion of the feces. This represents a classic conflict between the id, which derives pleasure from expulsion of bodily wastes, and the ego and superego, which represent the practical and societal pressures to control the bodily functions. The child meets the conflict between the parent's demands and the child's desires and physical capabilities in one of two ways: Either he puts up a fight or he simply refuses to go. The child who wants to fight takes pleasure in excreting maliciously, perhaps just before or just after being placed on the toilet. If the parents are too lenient and the child manages to derive pleasure and success from this expulsion, it will result in the formation of an anal expulsive character. This character is generally messy, disorganized, reckless, careless, and defiant. Conversely, a child may opt to retain feces, thereby spiting his parents while enjoying the pleasurable pressure of the built-up feces on his intestine. If this tactic succeeds and the child is overindulged, he will develop into an anal retentive character. This character is neat, precise, orderly, careful, stingy, withholding, obstinate, meticulous, and passive-aggressive. The resolution of the anal stage, proper toilet training, permanently affects the individual propensities to possession and attitudes towards authority. This stage lasts from one and one-half to two years.
i copy pasted that.