Nick Willis has caused coach Ron Warhurst a few grey hairs over the last 15 years, and managed a few more in qualifying for the world athletics championships 1500m final in London.
Running in the second of two semi-finals on Saturday (NZT), and with only the first five earning automatic qualification, Willis clocked three minutes 38.68 seconds in finishing sixth.
But he eased through into Monday's final as one of the two fastest finishers outside the top five in both semis.
Warhurst said 34-year-old Willis's unusual tactics - pushing the pace near the front of the field rather than staying out of trouble at the back - had caught him by surprise.
"As usual Nick always makes it interesting no matter what," Warhurst said.
"Usually he likes to run from the back but I think he wanted to make sure that he wasn't getting kicked around or anything, and just to make sure he got in.
"He doesn't run well from the front so I don't think you'll see that tactic on Sunday (London time)."
Willis, who won silver over 1500m at the 2008 Beijing Olympics and bronze in Rio last year, is contesting his sixth world championships, with his best finish a sixth place in 2015.
He's still working his way back into form following a post-Rio break, however, with chronic shin splints restricting his bid to post a qualifying time until late July.
Willis has a season's best of 3:34.74, but hasn't had enough track time or racing to approach his all-time best of 3:29.66 from 2015.
Warhurst says Willis still has the capacity to feature in the final.
"I wouldn't put anything past him, he's surprised people before both good and bad," the American said.
"It's all a matter of where his mindset is at for this one."
Willis has a day to rest up and work some spring back into his step, then will join Warhurst to work out a plan for the final.
"We'll go over the race and look at who's in it and then make the final decision how he's going to run it.
"I think the best thing for Nick is stay in the back and watch it unfold."