The object graph can easily be different from run to run depending on user input, timing, etc. Say, in the first run, the graph has a large subgraph due to a runtime condition (a property is set to a certain value), and on the next run, the graph is more lightweight because the property was not updated. It will take different amounts of time to collect such graphs (especially if they have destructors). I don't see how GC is any different here, it also depends on input, timing, etc. It's true though that a programmer has less control of GC because the rules when it is triggered are not always 100% clear (implementation details of a particular runtime) but imho they are as deterministic as RC; RC is just a form of GC which has very simple rules which are eaiser to understand.