What is the singlemost important skill a baseball player needs to be successfull in the MLB?

My first response was hitting but there are plenty of solid D, light hitting players who make a living.

I also thought raw altheticism but that's pretty vague and plenty of prospects have had top shelf althetic skills but couldn't get it all together.

I settled on timing. The timing to hit the ball, catch the ball, throw the ball (including pitching) and run around the bases has to be spot on to rise to the top in MLB.