An example of how perfectivity~imperfectivity work:
Everyone knows (?) that English converts an imperfective verb to perfective via particles; these perfectivized verbs are known as phrasal verbs. E.g.
The resentments built over time ~ The resentments built up over time.
The first calls forth an undifferentiated mass of resentments piling up where as the second calls forth a picture of individual cases or incidents which caused resentment and those cases piled up, one on another, as differentiated units.
The latter is classic perfectivity.