Antonyms for the phrase "be a foundation for" include "detachment," "disassociation," and "separation." These words suggest the opposite of being something fundamental and necessary for the success of another thing. Instead, they describe a state of being removed, disconnected, or isolated from others. Other antonyms might include "destruction," "disintegration," and "decay," as these concepts suggest a breaking down or deterioration of something rather than a solid, dependable base upon which to build. These antonyms provide a helpful contrast to the idea of being a foundation for something, highlighting the importance of connection, stability, and strength in achieving success.