re: Tennis is the most difficult sport to master

No way. My vote goes to golf. You start off on a well manicured tee box and hopefully hit the ball in the fairway.

OOPS, you're now in the rough that can be 3+ inches higher grass and not manicured, or behind a damn tree. Hit the ball and hope to get close to the green, but you may find a sand trap or the ball may find water in the shape of a pond or stream.

When you finally get to the green, it is a relatively large expanse of beautifully manicured grass with undulations, slopes, soft and slow when wet and harder and faster when dry.

And you have 4 strokes on most holes to make par.