If you remember someone having a name "like Megan," it's going to be hard to shake the actual name out of your head. If you think that the diabolical Count is the murderer in an Agatha Christie mystery, it's going to be hard to think of anyone else committing the crime even if he's shown to be innocent. If you're pretty sure you left your keys in that one old jacket you have, you're going to keep circling back to it because it's hard to think of other places your keys might be.
That's not the congruence bias. The congruence bias so completely dominates our minds that we can't even realize there are alternative theories. We can't find the real solution because we're not looking for it. One researcher tested this by giving people lists of numbers that followed a certain rule. (The numbers given were 2, 4, and 6, and they were simply ascending numbers.) People assumed that they were even numbers, or numbers that increased by two, which is a perfectly understandable guess, and not an example of bias. The bias came when people were told that their guess regarding the rule was wrong. Instead of thinking of alternate solutions, they began re-wording their guess. The problem couldn't be with the concept they'd thought of, just the way they expressed it.