Why do people hate the truth?

i am a realistic person. My friend asked me if his final project was good and i told him that it had some grammatical errors he got pissed off. My other friend and i went shopping to buy a dress, and she asked me if she look good in it, and i told her that she didn't but in a nice way, i even suggested other dresses but she got angry. How come people get mad when i say the truth, i mean come on isay the truth and a respectful way. I didn't tell my friend that his project sucked, i didn't tell my friend that she looked fat in the dress. I just said "no it doesn't look good, how about you try this beautiful black dress, i think you will look great in it." why do people hate the truth?