1. The first four shots in tennis are: the Serve, the Return of Serve, the Serve Plus One, the Return Plus One.
2. The most common rally length in tennis is: 1 shot!
3. 70% of all points at all levels of play end in the first four shots.
4. That is only two shots for each player or side.
5. 91% of all winning points in matches are within 0 to 4 shots.
6. The psychological reason that this is not intuitive to us is because the human mind tends to remember the spectacular and lengthy rallies.
What this means:
1. The top priority in practice should be the Serve and Return of Serve.
2. Of these, the quality of Return of Serve distinguishes the best from the rest.
3. The highest premium should be error-free tennis in the first two shots - Serve and Return of Serve.
4. Thus, the tennis athlete's primacy should be: perfect technique on the Serve and Return of Serve and attacking the Second Serve.
-- Craig O'Shannessy, World-Class Coach and Analyst for ATP World Tour, New York Times, Wimbledon and Australian Open, BrainGameTennis.com (from U.S. Tennis Congress, October 2016)