API problems that make life difficult for implementations

 - exposing unnecessary implementation details
 
 - making promises that are hard to keep
   - real-time promises
   - promises about the order of operations - prevents future concurency
   - overspecifying precision of results (returns the number of nanoseconds since the file was changed)
   - returning a data structure that promises to remain up to date indefinitely (leaking live objects)
   
 - factory methods: specifying that it "returns a new instance" rather than "returns an instance" - prevents future caching/pooling
 
 - specifying the whole truth, rather than just the truth
 - specifying all failure cases (instead of "reasons for failure include...")
 - Specifying that an enum or similar pool of types is a closed set - prevents adding entries later (eg: resource types)
 - specifying precise data structures of return types (HashSet, rather than just Set or Collection)