Ask HN: What was your greatest challenge in financing your venture(s)?

I'm a senior in the business program at CSU San Marcos. In one of these classes, "New Venture Finance," we are to ask a couple of entrepreneurs of various backgrounds about their adventures securing financing.

For this assignment I would most like to hear war-stories, tips, gotchas, or whatever else you might feel like sharing, with regards to how you financed one of your ventures (successful or not, I don't care). If that prompt is too broad, then perhaps you could share a bit about your greatest challenge in financing a startup?

This is a short assignment, and this Q&A is only a part of it, so rest assured I am not secretly trying to find someone to write my paper for me. I've had my eye on the tech startup world for some time (and I read HN daily), so I am personally interested in the discussion that (hopefully) ensues.

Thank you for responding :-)