[open] the floodgates

to cause strong and overwhelming emotional reactions, often leading to a burst of tears, feelings, or memories

The idiom "open the floodgates" originated from the literal act of opening the gates of a dam or reservoir to release a large volume of water rapidly. It can be used to show the release of long-restrained emotions, such as when someone finally expresses their long-suppressed feelings, leading to an outpouring of emotions.

After years of keeping her pain bottled up, she finally confided in a trusted friend, and the floodgates of her sorrow burst open.
The heartfelt eulogy at the funeral opened the floodgates of emotion, leaving not a dry eye in the room.
Watching the heartwrenching scene in the movie, the audience collectively opened the floodgates, with sniffles and tears filling the theater.
When she heard the news of her beloved pet's passing, she couldn't hold back her tears and opened the floodgates of her grief.

(of an action or decision) to allow for many possibilities, particularly those that were previously unavailable

The idiom "open the floodgates" originated from the literal act of opening the gates of a dam or reservoir to release a large volume of water rapidly. In its figurative sense, it is used to imply that an action or decision allows for many possibilities, particularly those that were previously unavailable, much like a sudden, uncontrolled flow of water.

The company's new policy to allow employees to work from home opened the floodgates for a more flexible and diverse workforce.
Lowering the interest rates on loans may open the floodgates for more people to invest in real estate.
The release of the affordable smartphone opened the floodgates to a broader market of consumers who could now afford the technology.
The government's decision to reduce trade barriers with neighboring countries is expected to open the floodgates to increased international commerce.
The announcement of a scholarship program for underprivileged students will open the floodgates of educational opportunities for many young individuals.