Some better reasons to celebrate on this day:

• Battle of Mantinea 362 BC, Sparta and Athens got fucked, never recover
• Battle of Hattin 1187, crusaders got fucked, never recover
• Battle of Kursk starts, 1943 Germans got fucked, never recover
• Zimbabwean War of Liberation starts, 1964, settlers got fucked, never recover

Overall though much more shitty things happened, bad day overall.