BLUF: At what point do I no longer take the time to invest in that relationship when the other party never responds.
I have taken Mark & Mike's advice for years on staying in touch with people and maintaining relationships. Most of the people on my list are at a quarterly frequency.
Several people who I stay in regular (quarterly) contact with do email or call back. Others never do. About 25% of the folks on my list never respond. I am trying to determine if it is time to lengthen my frequency of contact or simply prune these people off my list.