The picture of Longmen comes from the ancient legend that the Yellow River carp jumps over the Longmen (referring to the Longmen at the narrowest part of the Shanxi-Shaanxi Grand Canyon where the Yellow River roars down from the hukou, now called Yumenkou) and becomes a dragon.

It means that if you jump the highest threshold, my career will be successful, and if you go through the most difficult hardships, you will be rewarded.

Carp yue longmen is impossible, so it's just a hope.