The past simple is mostly seen as complete. This means the action or state described has finished, and can no longer change, with no direct effect on the present.
Another area that can cause confusion is when using states. For verbs showing states, for existence, possession and senses (such as be, have, seem, look, sound), the past simple is used, even for temporary or ongoing actions. I was happy before the phone rang. (not I was being happy) He seemed angry when we saw him at 4pm.