Face masks cut disease spread in the lab but have less impact in the community. We need to know why

In controlled laboratory situations, face masks appear to do a good job of reducing the spread of coronavirus (at least in hamsters) and other respiratory viruses. However, evidence shows mask-wearing policies seem to have had much less impact on the community spread of COVID-19.

Why this gap between the effectiveness in the lab and the effectiveness seen in the community? The real world is more complex than a controlled laboratory situation. The right people need to wear the right mask, in the right way, at the right times and places.