When you say "Thank you," you complete something. You are finishing a transaction, a relationship, a process. "Thank you" is like "good bye." You can complete all transactions at a surface level, but deeper inside is only one-ness.
Thankfulness always exists in relation to something else. You don't thank for nothing at all, you thank for something. But in this case, something is less than nothing!
At the deepest level, thanking has no meaning. Does one hand thank the other hand? The deeper you go, you see there is no "other" to be thanked.