Karolína Plíšková won her fourth title of the year, and 15th of her career, at the Zhengzhou Open this week and is now just 86 points away from the world's number one Ashleigh Barty in the rankings.

Yet, despite her incredible form this year, a Grand Slam title continues to elude her. After reaching the final of the US Open in 2016, she has not made it to another final.

There are obvious difficulties in transforming success on the WTA tour to the majors in terms of mental strength and courage, but this decade has seen a number of players show brilliance on the regular tour and not convert that into a major title.

The ever-changing keys to the world number one ranking

Since the start of 2010, ten players have navigated their way to the pinnacle of the women’s game and reached the number one ranking.

The rankings started in the mid 1970s and only the 200s have seen more number ones across a 10-year period.

With US Open winner Bianca Andreescu shooting up the rankings this year, after starting at number 152 in January, she could become the 11th player to become officially the best player in the world this decade.

When looking at this decade, Serena Williams has the numbers to suggest she has dominated with her 12 major titles. But after Williams completed 186 consecutive weeks at number one in September 2016, the top ranking has changed hands 14 times.

2017 saw five players become world number one at some point in the year but two of those players, Plíšková and Simona Halep at the time, had not won a Grand Slam before reaching the top.

This is a trend with certain players every year who reach world number one, so what does it take to win a major title?

The tournament before a major is not as important as it seems

There is the perception that for a player to make the breakthrough at either Melbourne, Paris, Wimbledon or New York, they must show good form in the tournaments beforehand and have experience of winning titles.

Yet, if we look at the statistics since the start of 2016, only once did a Grand Slam title winner also win the tournament before.

Andreescu won the Canadian Open this year as Williams had to retire, but otherwise nine players who have won majors in the last three years have not won the preceding tournament.

When looking further at the tournament results, on only four occasions did the winner of a Grand Slam since 2016 reach the final of their preceding tournament.

So maybe players like Pliskova, at least in the lead up to major tournaments, should not focus on results but rather how they feel on the surface they are going to play on.

Above all, mental strength is still the key difference

Halep is the perfect example of a player who showed immense fortitude on the WTA tour, but could not get over her Grand Slam hump.

Coming into the 2018 French Open final, she had lost all three of her major finals and in the previous year’s final in Paris, she lost to Jelena Ostapenko despite being a set and a break up.

In the 2018 final, she was coming up against US Open champion Sloane Stephens and found herself a set and a break down. In spite of all the odds being against her, she found a way to break the shackles and lift the Coupe des Mousquetaires (French Open trophy).

After the match, she said the win gave her new found belief that in the biggest of matches, she could win even if everything went against her.

Therefore, players like Plíšková may need matches where everything goes against them in a major and they still find a way to win. That may be in the first round, but that will likely give them immense confidence to make it to the next level.