[kimdcmason]

All of these seem sensible except "Avoid the pursuit of happiness. Seek to define your mission and pursue that."

"Your mission" is simply a placeholder for what you believe will make you happy. It's very subject to change. I'd argue that a healthy respect for what makes you happy can help you avoid a mission that you'll later regret.

[yesenadam]

It seems sensible to me. (It's a huge subject but:) I think he's referring to the well-known paradox where aiming directly for happiness doesn't work; instead going for meaningful goals that will give satisfaction does. Asking "Am I happy?" constantly stops you being so. etc.

>"Your mission" is simply a placeholder for what you believe will make you happy.

Simply?! Well no. Even without that, it doesn't seem right. I think I know what you meant, (like I think you know what he meant) but the two aren't always equivalent. Some people have important and unattainable goals that they know won't make them happy. Or doing your duty, like taking care of sick family etc. More to do with meaning than happiness. It sounds like you would argue no-one can do anything but what they believe will make them happy.

And Socrates and Kierkegaard etc realized that often in life we would regret either of two choices. The grass is always greener, and feeling regret doesn't mean the other choice would have been better. (e.g. To marry or not)

[placebo]

Yes. Another way to look at it is the bottom line of various non-dual/mystical teachings which is basically that the best way to achieve lasting happiness is to eliminate the seeker of it (of course, not in a physical sense) - or put more accurately, to realize that the very illusion of the personal self is the root cause of the unhappiness.