Question

Why should maximum percent yield never be above 100%

Answer 1

You can't have more than you started with.

Answer 2

there will be no such thing as IDEAL condition to get the perfect 100% yield. :)

therefore, getting a 100% and over is impossible. you can never get 5 apples when you add 2 apples with another 2 apples.

*copied from the other question. :P*

Answer 3

percent yield = (actual mass obtained from experiment /calculated
mass obtained from chemical equation) * 100%
SO IF NOMINATOR =DENOMINATOR THIS WILL GIVE 100% yield but in real
the NOMINATOR don't exceed DENOMINATOR because of loss in mass of
the product due to side reactions ,collecting method ,...etc
so the percent yield always less than 100%