I think about this in regard to my own teaching. Quite often, the students who seem to benefit the most from my teaching are those who have already been attuned to learning through the work of their parents or great teachers from their past. There are a few occasions where I know that I played a critical role in a student's love for learning, but it seems to be more frequently the case that I am reaping what someone else had sown earlier. This really comes to mind when I have parents thank me for the work that I’ve done with their child. I often thank them right back for the fact that they had raised a child so open to learning.
This is true in many of our relationships. We are regularly reaping the rewards (and sometimes the responsibilities and pitfalls) of our relationships due to elements from the past of which we had no part. This is true in the reverse, as we frequently bring to our relationships both tools and baggage that we gained from earlier experiences, most of which our friends might know nothing about.
For that matter, we should think about the “seeds” we might be sowing now but will never have a chance to reap. What we put out into the world might not necessarily come back to reward or punish us at some point in the future. However, someone will have to deal with the consequences or rewards from our actions (and inactions).