If you want to be a bad product manager, only focus on the short-term. Spend all of your time working on the next release and the sales goals for this quarter. After all, if you can’t get through this release/quarter, everything beyond that won’t matter. A 3-year plan? You might not even be around in 3 years! You need to hit your short-term targets, because that’s what your bonus is tied to, and everything else can wait until later.
If you want to be a good product manager, think in context of the long-term. Yes, the next release and sales goals are important, but there are other people focusing on the next release (developers, project manager) and sales goals (sales, marketing). Most likely no one else is thinking about the future of the product.
Only looking a few weeks or months ahead leads to habitual fire-fighting. You can never get ahead of the curve and become a market leader. By taking a step back and looking at your product with a longer timeframe in mind, it will be much easier to plan your near future.
It’s always difficult to pull yourself out of the day-to-day and think about long-term strategy, but it needs to be done. If you complain that you don’t have enough time to do this, then that’s even more of a reason that it needs to be done — the reason you’re probably so busy now is because you haven’t devoted enough time to long-term planning.
There’s no good excuse for not looking at the roadmap of your product. It will help you as a product manager plan the tactical activities needed to execute on that strategy. It will help towards building a successful product that has a future, which in turn helps all of those who contribute to and use the product.