When my sisters leave me out, what are they trying to accomplish?

im the youngest and i understand leaving people out causes bad feelings. so why do they leave me out? how could someone be so silly to think it wouldnt hurt someone? subliminal messages, looks and education are the constant things. almost daily. i love them but this upsets me, i have enough respect to see that u only live once and that is rude and i didnt do anything bad to deserve it.