I've been reading up on gaps. I read about the three main types of gaps and generally where and why they might happen. But I'm not really getting why alot of traders feel a gap 'must' be filled. Read something else about if a gap never fills then people aren't sure if a trend is really ended or something to that effect. But I don't get that. What exactly are the consequences if a gap never gets filled?

Saw somewhere that someone said that's actually a myth and that it's not technically true that they must be filled, but that generally traders "abhor" gaps. They hate them in other words. Why? And why do people want them to be filled?