Press the green flag
Credits to bungie and 343 for Halo, and credits to Lucas King for the music. If you look at the Master Chief after Cortana "Died" you'll notice that he tried to lose himself in his work. He and Blue Team were doing missions back to back. No rest. Just nonstop work. He was trying to revert back to the emotionless machine from Halo: CE. He was trying to become Hollow to cope with his loss. Heavy Stuff :'-(
