The truth or feeling good?

This time we have one difficult, it's better to say the truth or don't say it because can hurt somebody?

I remember once when I was little that I lied to my parents because I behaved bad in the school, and I was afraid because I thought they would be mad, but that don't happened, they just hugged me and told me never to tell lies. They did not care that I behaved badly, they were worried because the lie. So then, I never say lies anymore... And that is a lie. 

The truth is and I always said, I lie or hide something like all the time. If a friend tell me something that he/she did it, I can say it because is not my secret even if it is awful or hurts someone, I just can persuade so he/she tell it.

When is about me, like I hide something, I think that when is not important or hurts nobody isn't a big thing lie or hide things, like if I say I cleaned my room but did not or if I said that "I'm almost there" but actually I just woke up. These are thing that will be forgotten almost inmediately (maybe I fight a little and be punished but is not a big deal). BUT and this is the supreme but, If the situation is important or harms someone, you always must to say the truth. Most of the time, hide something or don't say the truth it´s the worse that you can do because maybe someone can help you or it gets worse and also, usually the people get upset when they find out that you lied, even more that the situation for you lied.

So, what do you think? Should we always say the truth?