Ignore what I have already spent

Deciding whether to continue something you are deep into.

I have put a lot into this and I am not sure whether to continue. Ignore everything already spent. Judging only from here, is continuing the best use of the next three months? If the answer is no, say it plainly and tell me what stopping would cost.

Context:

Assumptions and reasoning. Digging out what you are taking for granted, including the sunk cost you keep not naming.