How far can you take the truth

Ok so teachers an adults always not to lie and tell the truth but sometimes telling the truth can hurt your friends and peers. If you always tell the truth it's not going to always have the best outcome for example if a friend ask your if you there hair is looking good today and it doesn't look the best sometimes the best way to reacte is to say it looks good. I'm not saying always lie and that lieing is ok I'm just trying to say that you can't always tell the truth