Okay, so it's deemed one of the biggest clichés ever, but think about it...
If everyone spoke truthfully and acted honestly, how could there be room for doubt and misunderstanding? No misunderstandings would mean no unnecessary squabbling and that would leave room for just happiness :)
Yes, being honest might mean hurting someones feelings, but on a much smaller scale than it would if you lied to them! Nobody wants to be lied to.
And "Ignorance is bliss", have you met "Knowledge is Power"?
So I dare you! Try to go through a day without hiding your True feelings and intentions. Be honest. Can you handle it? ;)