My pal Jim Holland has a nice post on getting started--and maintaining your relevance--in product management. You have responsibility and accountability. But market knowledge is the source of authority.
I recommend product management start with Market Authority.
Market Authority is the foundation of sustainable product vision and all the moving parts that follow. While I placed Product Vision first in my post, I stated, “Product management has a great influence on product vision. Driving strategy as a leader begins with knowing your markets.”