They act as a perfect description for the often wavering game of Alexander Zverev, who can go from outclassing the world’s best players and winning Olympic gold to being unable to land a serve in.
When he last faced Andy Murray at the Cincinnati Masters last August, the German’s second serve almost completely vanished as a useable shot.
He has had worse capitulations with ball in hand on the service line but the hope for Murray when the pair meet again in the third round of Indian Wells on Tuesday night is that memories of that encounter still weigh heavily on his opponent.
There have been positive signs of the physical rather than mental rebirth of Murray in recent weeks – his fightback to beat one of the game’s rising stars in Carlos Alcaraz in the previous round a particularly pleasing tonic to some previously tough defeats.
But he faces a step-up against Zverev, the No3 seed and a recent US Open semi-finalist.
Casting his mind back to their last encounter, Murray said: “The match that we played last year, I’m not saying he was playing his best tennis at that stage but he did make the final of the US Open a couple of weeks later.
“I wasn’t physically feeling particularly good and did not play particularly well but managed to win. From that perspective, I can gain confidence knowing that, if I play a really good match, I’ll be in there with a shot. He’ll certainly go in as the overwhelming favourite but, if I play a high-level match, I’ll be right in there.”
With relatively little tennis in his legs compared to the likes of Zverev in recent months, the question is always around Murray backing up a good result as against Alcaraz. Too often against higher-ranked opponents, being match shy he has understandably faded – but the confidence is building.
“I’m starting to get there again and get to a level where it wouldn’t surprise me if I won a tournament,” he said. “Playing with a metal hip is not easy but I do genuinely believe that I can win tournaments again and have big results against top players.”
Murray readily admits he and Zverev are not “best friends” ahead of their meeting and had pushed the ATP to create a domestic abuse policy, which has since been adopted.
For his part, Zverev welcomed that same move amid an investigation into allegations of abuse by his ex-girlfriend Olya Sharypova, which he vehemently denies.
Cameron Norrie, meanwhile, continued his fine 2021 as he knocked out Roberto Bautista Agut in a third-round match that went late into the California night.
The British No2 beat the Spanish No15 seed 6-4 5-7 6-3 to set up a last-16 encounter against Tommy Paul, who was a surprise three-set winner over fourth seed Andrey Rublev.
Dan Evans, meanwhile, let slip a one-set 4-2 lead as he lost 10 subsequent games against Diego Schwartzman in a 5-7 6-4 6-0 defeat.