Objects need to collaborate and interact and depend on each other, but it's important to maintain healthy boundaries. Other objects are not allowed to touch your private parts, and you get to say what is visible and what is not.
MultitaskingObjects must know how to handle multiple requests at once while maintaining their state.
Grace Under Pressure
Well-designed objects need to be able to handle stress and overload.
Honoring your commitments
Objects provide public interfaces, which provide an agreement as to what they are willing to do. You can not change your agreements without talking about it first.
No object is an island unto itself; all objects have dependencies on other objects. But an object should not be overly dependent on others, as this means it becomes fragile to changes made in the other object.
However, it's important to recognize there are some OO principles that should not be applied to relationships.
Single Responsibility Principle - each object has one and only one responsibility in a system. Shyeah, right.
Pluggability - you should be able to replace one object with another that plays the same role. No thanks.