You'd find no universal definition of a PM. You might translate it into "Product Manager", "Project Manager", or a more beautiful one: "Profit Maker."
But as I know, a good PM is a "Planning Machine", vice versa, a not-so-good PM, generally, is a "Problem Manufacturer."
Since PM acts as a leader of a product or a project, PM should pay more efforts on planning:
1. Make sure how many resources on hand.
2. Set up the goal of the product/project: Performance, Growth rate, Revenue, Relationship building, Market plotting....or maybe some other strategic concers...whatever the goal is, clearifying is the first & most important step.
3. Presume all the difficuties this product/project might encounter and prepare for back-up solutions.
4. Measure the risk and try to lower it.
5. Predict the Market trend and absorb industrial info.
6. The last but not the least: Never design an existing product.
Theoretically, well-made plans are necessary for a product/project.
But practically, most PMs don't have mature mindset to plan well. (esp. me QQ)
It's a sad sotry, and never ends.
