Jack of All Trades, But Master of None

That's me, I think. I've tried so many things... been relatively good at them at the start, but never really followed them through till the end to really master any particular skill! How terrible is that?!

I could list down all the things I've tried... Now where should I begin?

Sports: Tennis, badminton, ping pong, squash, swimming, pool
Jobs: Accountancy, Computer Science, Actuarial
Others: Piano, Treasure hunting, Dance, Yoga

For all the above, the first time I tried them I caught on pretty quick. I was even quite good at some of them. But later on, when the learning curve picked up... to really excel in anyone of them, I just lost it. Like there's only a limit on how well I can do in each one of them.

So, how bad is it to be a 'Jack of all trades, and Master of none'? Is it better to know how to do a lot of things relatively ok, and not particularly excel in anything? Or to focus on one thing that you can be a Master in?

For jobs, the goal is obviously to be a Master of your own trade. That's when you know you've really succeeded. But how many people can actually do that successfully? At motivational seminars, they always tell you to reach for the stars, to reach your maximum potential. But what if your 'maximum potential' is still not being a 'Master'? Does that mean, in effect, that you have failed??