I always considered it as reciprocity. For instance, if I do something for another that inconveniences myself it is with the expectation or knowledge that they would do similar should I ever be in a situation that requires assistance. It's not quite the same as considering that they are indebted to me for it. I do not keep a tally. There are some friends who need more than others or more than I do and some who require less.
If reciprocation, however, does not occur then I am no longer willing to provide what I previously would have. There are exceptions to this of course, as people often have many things going on and I know that I personally can't always provide some people I care about with the time and attention I would like to give them. This isn't held against an individual, but blatant disregard of previously held expectations without due explanation alters the dynamic significantly and often irreversibly.
Thinking about all this now, I probably operate more on a "treat others how you expect them to treat you" standard than by the "golden rule".