When there is some rare dxpedition, many ham radio will try to work with that station.
if you hear on their operating frequencies, you will hear bunch of pile up call from around the world.
How to break into their pile up calls?
for CW or SSB operation, you can try to transmit a little bit higher or lower than their receiving frequency.
If you transmit higher, they will easily listen to you call because of your signal sounded a little bit narrow or higher pitch than others.
Depends on their receiver filterations too if they use narrow filter, your signal probably cannot be heard at all. The best technique is to have a bigger gun and higher gain antenna than others.