You're the only one arguing, I'm just fixing grammatical errors. You're much too accusatory and vain, be more reflective and critical and it will get you much further in life. Just read what I wrote below and think about it, you really don't need to respond.

Without the comma, the complete sentence: "Stop accepting that what you expect is what should be." is an independent clause.

"Stop accepting that" is an independent clause. "which you expect is what should be" is a dependent clause that gives more information on what "that" is. "which you expect is what should be" refers to "that", since "that" was previously mentioned, you use "which" as the determiner, not "what".

"What you expect" refers to infinite possibility.

That's not part of the definition, I'd challenge you to find a single definition of "what" that phrases it that way. "What" is a determiner used in specifying something, refering to the thing or things that. "Which" is a determiner used to refer something previously mentioned when introducing a clause giving further information.

"That which you are trying to express" is very specific.

And if you can understand why "which" is the right choice there, you should be able to understand why it would also be the right choice in the sentence we're discussing

"What" refers to infinite possibilities.

"Which" refers to limited possibilities.

Again, there's a severe lack of logic behind your words, you're still operating solely on arbitrary beliefs. None of this infinite/limited possibilities stuff you're rambling on about is part of the definition of either "what" or "which". Once again, I'd challenge you to find a single definition of either that phrases it that way.