Why?

[Shanoonlk]

jeden Tag ist genau das gleiche!!

[Kebap23]

jeder Tag ist gleich

[McSupreme]

The sentence you wrote means -> It's the same every day(, the weather is bad, i'am tired and hungry). -> "Jeden Tag ist genau das Gleiche(, das Wetter ist schlecht, ich bin müde und hungrig)" Because of the article you have to write the G of "Gleiche" as a capital letter. The sentence that Kebap23 wrote means: Every day is the same. (equal). Got it? Greatings form Germany :)