"Fixed deadline, negotiable scope" has to be the most underrated pattern in product management. It's the secret to shipping.
It's not too hard to come up with a feature. The hard part of product design is sewing many features together into a coherent whole.
Theory and practice are asymmetrical. You can learn theory from practice but you can't learn practice from theory. No shortcut to practice.
The best product development and coding processes preserve your ability to make decisions later when you have better information.