Why do teeth come in wrong?

Genetics: And premature loss of primary teeth, as well as parafunctional habits like thumb sucking or using a pacifier for too long. You can control most everything except the genetics.

Size discrepancies: When teeth come in "wrong" [fancy doctor word, ectopic eruption], it is usually because there was no room for them. Human teeth will take the path of least resistance, so if a baby tooth did not fall out in time for the adult tooth to come in, or if decay or extraction caused a tooth that was supposed to be there not be there, the subsequent erupting tooth will come in "wrong".

Malocclusion : Can result for a host of reasons. Can be genetic, skeletal, due to congenitally missing teeth, etc. Your dentist will advise you when its time to have an orthodontic consult. Hope this helps.