You will be ragged on relentlessly. Any character flaw you have will be targeted. You will be forced to do degrading tasks and asked to thank your Drill Instructor for more of them. You will go without sleep for days on end, carry heavy loads, then given mental tasks to figure out.
The goal of Marine Basic is to break you down like an enemy would if you were captured. YOU won't exist. You will become a sleep-deprived robot. The physical stress is only applied to accentuate the mental stress. It's all about reprogramming your mind.
Your rack (bed) will be made to certain standards, which you will never meet. Your clothes wil be hung up in a certain manner, which you will always get wrong. Your brass (insignia) will never shine to standard, etc, etc, etc.
If you want someone to tell you how good you're doing, don't go in the military. All services will only focus on what you do wrong (even if it's right).