Did it (in the UK). Started a sole consultancy, grew it into a training and courseware business employing around 10 people. Formalised what was previously an ad-hoc partnership with a US-based organisation into a franchise-type contract in exchange for a five-figure marketing kickstart from them, and tooled up (software and people) for a 'letter of intent' long-term joint contract with the US military in the UK for technical and personnel training, then found out that despite a written agreement, they were poaching our business in the UK. We started talking to them, they said we could forget the funding. We were small, they were corporate and basically told us to fuck off and sue if we had the cash to carry it through.

Had to fold the business. Nearly lost my house and marriage. This was in the late 1990s.

For every story, there's an equal and opposite one.