Definition
When a surprising or unpleasant fact or concept sinks in, you slowly begin to understand, accept, or comprehend its impact on you.
When she heard the bad news, she couldn't believe it at first, but after a few hours, the reality began to sink in.
The concept was complex for the students, but after several discussions in class, it eventually began to sink in.
The mistakes he made became clearer, and as he started to reflect on his actions, the consequences began to sink in.