I've been there, a client-side app I built in 6 months got a rewrite which took 5 people 2 years and ended up with about half the original functionality. The r

I've been there, a client-side app I built in 6 months got a rewrite which took 5 people 2 years and ended up with about half the original functionality. The rewrite was warranted because so much stuff (API, UI) was changing entirely due to external forces. What it actually did (from the user's perspective) was pretty similar, how it did everything needed to be different. I didn't write it myself again because I was busy with other stuff. There were numerous reasons it failed (we can say failed because the customer ended up going elsewhere). Devs were inexperienced, overconfident, chose inappropriate technology for the problem and wouldn't listen to advice. There was nobody in a tech lead position on the project (CTO at the time constantly spouted nonsense about "self organising teams") so everybody spent their time shaving their pet yaks and hoping other people would handle the difficult/boring bits. Deadlines were repeatedly issued but had no bearing on reality so everyone knew they'd be missed - thus they were meaningless.