I've worked for two startups that failed in entirely different ways.

Startup A: We built custom analysis software, a 1.5 million line-of-code C++ codebase with 2 major products.

Head count: 20

Reasons we failed (IMHO) - in order of importance

1) Heavily saddled with tech debt. 1.5 million lines of C++ code is not an asset. When we started Web technologies were simply not able to provide the kind of functionality we were offering. So we kept doubling down on the thick-client software. When the web finally started to catch up, we had the wrong skill sets in the wrong places to pivot the tech without rebooting the entire company. We hit a weird technology gap where thick client software was on the way out, but web tech wasn't quite up to par for most of our existence. Near the end it web tech stacks were probably good enough, but we ended up going down the wrong path.

2) When we did try to start over with a clean code-base our tech skills couldn't move to the kind of technology that was becoming fashionable in enterprises. So we built another desktop client very quickly in C#. It worked well, but it was like selling a different kind of horse in the age of the car.

3) Absolutely terrible sales staff. I learned more about how important sales teams are from this ride than from any other experience. Nearly 90% of the sales came from word of mouth, and the rest from a couple of us tech guys bird dogging it out on the street. 4 successive sales guys produced $0 of sales over 6 years. To make matters worse, none of them were ever able to gain enough proficiency with the software to sell it themselves, they always had to pull along a "sales engineer" to demo. Total mess, and it's made me pay much more attention to corporate sales apparati over the years.

4) Funding funding funding. Our total VC investment was too small, and our executive team too inexperienced to realize this. We easily needed 10-20x the investment to make it work, hire good staff, pivot to better tech stacks and approach the market correctly. When we started the VCs claimed that we'd be the next unicorn, the money never added up to make that claim makes sense.

Result: I rode the ship down because I was learning so much on the way. The people were good to work with so it made it worth it. Everybody ended up in good jobs elsewhere and we're almost all in senior or executive positions, applying the lessons we learned.

Startup B: Web-based analysis software (I can learn!)

Head Count: 60

1) Absolutely dishonest, immature, corporate leadership who couldn't work together to operate an elevator. Treated key employees like garbage and ignored the rest. It was like middle-school.

2) The bad behavior extended to customers, who were often put against each other by the CEO in a web of deceit. Hard to explain, but very bad behavior.

3) Tech looked awesome, the back-end was rubbish because the engineering team was incredibly poorly run. I mean like builds completely breaking every day, completely unscalable critical architecture components, senior engineers insisting pet projects be included.

Result: I fled like a deer stampede in a wildfire. The company closed shop not too long after I left and the CEO and some of the senior C-level staff have disappeared from the face of the Earth. If they're doing something, it's not public in any way these days.