Why are boys so confusing? (this is for everyone but I prefer boys)

In middle school and high school why do boys like to flirt with some girls but then they get shy with other girls and they ignore them and act like they don't like them when they do, it makes no sense
I mean their in high school and middle schools they should have the guts to go up to ANY girl and tellthem that they like them, or they think there cute
I WANT YOU BOYS TO TELL ME WHYNYOU GUYS DO THAT OR GIRLS TELL ME WHY YOU THINK THEY DO THAT