The perfective aspect is makes it so that the verb is viewed "outside" the verb, while imperfective verbs have an internal view into the verb.
This makes sense for past tense verbs, in order to view a past perfective (preterit) verb from the outside, it is already done, while past imperfective (imperfect) verbs just show something is in the past but have no indication that it has stopped (and therefor continue to have an internal view of it).
To say, "I walked," just tells the action but does not give any internal information about what happened during the process of walking. "I was walking," implies something happened during walking (stopped, hit by a bus, abducted by aliens, etc.), which gives interior composition, or "I used to walk," which implies that it was a continuous thing, giving an internal view into that as well.
This also makes sense for the future tense, "I will hit him," implies that the action will take place, but it does not give away any information about what will happen during that process, while "I will be hitting him," might imply that it would be continuous or something might happen in the process of hitting.
What I don't understand is how the perfective aspect can represent boundedness in the present (where a person would always have an internal view of it). If you are doing something in the present, it is continuous (and therefor imperfective), and the moment you talk about it without having any internal structure (perfective), it exists in the past and you are just using the preterit tense.