How to learn to get out of the saddle

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I have no idea why I can't do it...it just feels un-natural to me and I have poor balance, although I could easily do it as a kid. At this point I've pretty much given up on it.

I tried to stand the other day and made it maybe 3-4 pedals before I said screw it. My knees were angry.

I don't get it, though...like you, I could do it as a kid, no prob.