What is wrong with this premise?

[Darkstar]

By default I don't see why your premise should be true.
But can you specify what your definition of a cause is, and what you mean by something coming into existence.

I would accept the premise as true because in my experience everything which has come into existence has had some cause.

What in your experience has come into existence? And before you answer that question you need to very specifically define what you mean by 'come into existence' so everybody understands what we're discussing, and nobody tries to move the goalposts later in.