There's a high standard at the top of the men's game these days, which means a long road for those aspiring to get there.
It's one with stops and starts, fluctuations and plenty of required adjustments along the way. The field at this week's Miami Open is an illustration, marked by both withdrawals and comebacks from players leaving or returning to the challenge.
Many of the players who had been making upward strides coming into the season have found it difficult to keep up their momentum, particularly because of injury or inconsistency. A week ago at Indian Wells, US Open titlist Marin Cilic played his first tournament back from a shoulder injury and French Open semifinalist Ernests Gulbis picked up his first win of the season. Juan Martin del Potro stayed on the sidelines following more wrist surgery.
At Miami, the 26-year-olds are switching up: Cilic has withdrawn, Gulbis is looking for a second win to put his shoulder problems behind him and del Potro is returning to competition for the second time this season.
Cilic, who had been dealing with the injury before and since his US Open victory, also withdrew from doubles with partner del Potro at Indian Wells.
"I didn't feel, you know, completely painless. Just I felt that it's a bit rusty still," Cilic said following his singles, having only been practicing for three weeks. "I wasn't able to do any tennis. I had to rest completely from playing, and I was doing only physical in this part."
The Croatian is now looking for more matches, saying "I think I'm going to be soon in pretty good form," but first must return to tournament play.
Gulbis, another player who has been experiencing a chronic shoulder problem following Wimbledon, also recently stopped working with his coach and after six straight losses to open the season, finally won a match.
"I was relieved," Gulbis told ESPN.com. "That was the only emotion I had the first hour, and then I was happy. I just started to practice well since I came here. I was really motivated to start, I did a lot of fitness, I did a lot of tennis -- and it paid off. At least I won one round, so we start there."
With physiotherapy, the injury is now under control, the talented but erratic Gulbis is now looking to start picking up wins regularly again, saying, "I managed to put it in decent shape. It's still not 100 percent, but it's getting there every week. And that's the main reason why I couldn't be consistent, just because of lack of hours on the court."
With Gulbis, training is now even more important than competitive play.
"I need a lot of practice," the 16th-ranked player said. "And then with one match, I can turn around my confidence level."
But it's del Potro who has really been on the injury roller coaster, with the Argentine returning at the beginning of the season from surgery on his left wrist. Though he won a couple of matches in Sydney, he could not play the Australian Open and had a second surgery from which he is now coming back.
For now, del Potro is just concerned about getting back on court, especially in the tournament's Argentine-filled stands.
"I always wanted to win another Grand Slam, be top three, maybe No. 1," the 2009 US Open champ said. "For now, I'm happy to play my first match.
"It doesn't matter if I will be top 10 or top 100. I don't care about ranking. I just want to hit my backhand without pain and finish my match healthy. If I win, even better."
It's much the same through the tour. Milos Raonic reached the semifinals of Indian Wells, while fellow up-and-comer Grigor Dimitrov is looking to get a grip on his game and a new racket. Last year's US Open runner-up, Kei Nishikori, is not quite finding the big wins he was the previous season.
A couple of Frenchmen are also looking to get into the swing of things in Miami. Jo-Wilfried Tsonga will play his first event of the season in Miami and Gael Monfils will return from an injury this week. However, Richard Gasquet has withdrawn with a back injury.
As for the Aussies, teenager Thanasi Kokkinakis is coming off a couple of big wins at Indian Wells, but Nick Kyrgios' rolled ankle and Bernard Tomic's back will keep them both from playing Miami.
These list of maladies are part of the game -- but so is recovering and playing through it, according to the approach Gulbis is taking. Even the likes of Roger Federer, Rafael Nadal, Novak Djokovic and Andy Murray have had their injuries, but they've all returned to pick up where they left off.
"It's just a chronic tennis player thing, which I learned how to handle," Gulbis said. "And the top players have learned how to handle their problems as well. Everybody has some problem they are learning how to handle."