Don't take anything too seriously but what you contribute to something, mainly your work and what you do for the people who matter to you. For those two things go the extra mile and do whatever it takes, for everything else relax and enjoy yourself. It's tough to be serious and fun, but I think we can all walk that line. I am a little too serious most of the time.
It seems to be common practice to not take your work seriously. Not taking your work seriously not only hurts you, your family, and your friends; it hurts your company's customers, your city, your country. The entire world will be lessened by the sub par work that you choose to do. It's not just one bad worker or one bad company, but everything we buy, everywhere we go, everything we experience will be lower quality if no one cares. People don't see the result of their actions, you have to pay it forward and do the best work you can and not just for yourself.
For a lot of people you know, the most good you can do for them is to challenge them. People will not become better if their life is nothing but easy. I see a lot of people taking it easy on the ones they care about, but that isn't the best thing for them. I believe they are hurting the ones they love by taking it too easy on them.
I see this in public a lot, a 5 or 6 year old is crying in a store and the parent bends over backwards to get them to stop crying. The parent doesn't realize that no one else will bend over backwards for them. The children are becoming accustomed to something that only the parent will do for them. When their child gets around other people, the children won't know what to do because the other people won't think the children are the most important thing in the world and do anything to help someone else's child. =\ I've seen some people give attention to another person's whining child, but I think this is only reinforcing the bad behavior of the child and the parent.
This same rule applies to everyone. Someone who is so desperate to make you happy will typically not attract your attention.
(I think I've said too much.)