I believe most of the time this phrase is said to an inexperienced artisan who has no idea how the current system works, what's the shortcoming of it, and how to improve upon it. Think of an undergraduate student who tries to solve the Goldbach conjecture. Usually what ended up is either he fails to reinvent the wheel, or reinvent the exact same wheel, which has no value. The phrase certainly does not apply to professionals.
Even then, you know what's a good way to learn about how the current system works etc, maybe even the best way? I've got many failed projects behind me, and 0 regrets.
