How do you recover from funding rejection?

I have seen many founders struggle with fundraising. It's quite an unforgiving experience. One moment it's all hunky dory, you have interest from many investors, several even ask for a follow-up meet. A couple even hand you over a term-sheet. At this stage, founders feel fairly confident. Some even feel like they will now get to pick and choose the right investors for them. A day later, the due-diligence process starts. It starts with a few friendly questions, then some random data requests, followed by some critical questions and hush comments. You are expecting it end soon, but it doesn't. It drags on for weeks. And one day you realize that your start-up is considered un-investable for reasons that you can't fathom or never thought were important even worth considering. At this point you have already lost several weeks, your runway further reduced, and team enthusiasm significantly cut down. How do you deal with this?