Over time I’ve come to appreciate this more and more. The “loosely held” portion is important for allowing respectful differences of opinion and building a team together. But the “strong opinions” portion is equally important. You should be opinionated and understand why you hold those opinions and be able to defend them. But also learn to hear dissenting viewpoints and value them too.
Be strongly opinionated, but be comfortable with updating that opinion once you have new information.
Updating is the hard skill to master.
You have to be willing to separate ego from ideas and thoughts and be okay saying I was wrong or my idea/thoughts are no longer valid / the most accurate with this new information.
You also have to be willing to be curious and open to new information and counter points that will invalidate or weaken your opinion.
Be opinionated, debate like hell, but once new information is available be willing and okay with changing and updating your view if it makes sense.
Many of the issues I've seen in team engagements come from folks not being willing to dig deeper on their own feelings in an open setting. They end up passively resenting the path the team takes because their opinions are still very much a subconscious thing with poorly defined edges.