Hi,
let’s face it: DIY is based upon try and error. Sure, every now and then there could be done some math beforehand but usually it is too tempting to just do it, ride it and cry afterwards (in case it didn’t work the first time). And that’s what we love about DIY, right? Otherwise we would be theoretical physicists rather than MacGyvers, to put it in two extremes 
Nevertheless, whenever we are patient enough, we could also ask our community for their opinion about our latest brave idea before climbing on our rockets to see how it might work out. Almost always this would prevent us from burning some more or less expensive hardware. It would also spare the tears and the painful learning it on our own the hard way.
Why do we fall sir? So that we can learn to pick ourselves up.
(Batman Begins – Alfred Pennyworth)
Thus, I would like to have a thread, where we can share our failures, honest and proud.
**One would say for the sake of safety for others who could learn from one’s mistakes. Another would say, just for the childish joy of seeing things being destroyed 
You choose** 
I’d like to start with a mild example, where I destroyed my first belt on tape.
- Error consequence: belt got torn
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Reason: Belt was too weak for motor torque/power combined with crooked axes between pulley and wheel (motor mount was a little bit tilted)
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Explanation:
- I wasn’t patient enough, so I ordered pulleys and belt (9mm) before doing the math for the belt drive.
- Didn’t check the angle of the motor mount after clamping it to the hanger.
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Solution: I should have used a 15mm belt drive. I adjusted the motor mount angle and since then, no problems anymore.
Lesson learned 
made my day