I have just started learning game/graphics programming (with OpenGL) for a few days. Everything I know so far is very basic like camera, VBO, shader concepts,...I'm just very curious to know what common challenges/problems in game programming are to kinda estimate the time I will need to dedicate to my learning. My biggest goal at the moment is to make a decent looking 3d game with many open worlds and pretty looking shaders.
What are the challenges that I should be afraid of (or prepared for) the most to make that kind of game?