Sometimes things just don't go to plan on the court...
... and frustration starts to build.
But there's a place the WTA stars go to build their games and add new dimensions - the practice courts.
Eugenie Bouchard is one of the biggest proponents of hard work - she talks about it all the time.
And the hours she's been putting in off the match courts have been paying off big time the last year.
A year ago Bouchard was ranked No.93 in the world - this week she's ranked No.19 in the world.
Another one of the hardest workers on the tour is Angelique Kerber, currently at No.9 in the world.
Kerber went into the 2011 US Open at No.92, was No.32 by the end of 2011, and broke the Top 10 in 2012.
The German has been a mainstay in the Top 10 ever since, and Germany's No.1 player for a while now.
And she's the No.1 seed this week in Nürnberg, one of two WTA stops in Germany, alongside Stuttgart.
Speaking of Germans, WTA rising star Annika Beck has been making her home fans proud the last year.
Right after turning 20 in February, she scored her first Top 20 wins - over Bouchard and Sam Stosur.
Our practice court fanatics all scored passing grades in their first matches, starting with Beck...
Kerber won her opening match on Tuesday afternoon, battling past New Zealand's Marina Erakovic...
And Bouchard is already through to the quarterfinals - she won matches on both Monday and Tuesday.