So, reading here what I understand is that startup stocks/options/whatever are worth nothing because this is a private company, an opaque box with many tools to

So, reading here what I understand is that startup stocks/options/whatever are worth nothing because this is a private company, an opaque box with many tools to screw you. Anyone with a different experience? If you had a positive experience/return, what was the cause, your negotiation or the founders/investors behaviour?