A little too focused, sometimes.
Earlier this year, the promising cyclist was travelling along Dukes Rd, in Mosgiel.
He had his head down looking at his bike computer. Then he woke up "in the boot" of a car.
The 17-year-old John McGlashan student had ploughed into a parked vehicle.
Remarkably, he escaped with just cuts and bruises and a life lesson.
"I was back into it after I got all the bandages off and everything."
He spent the night in hospital under observation. He was extremely lucky.
It could have been so much worse than in January when he crashed his mountain bike while attempting a jump and fractured a bone in his lower leg.
He was in a cast for six weeks after that one.
But none of that has slowed the teenager down. The year 12 student carved up at the national secondary schools championships in Timaru recently.
When he stays on his bike, he can really make it hum.
The 60km road race was an exercise in determination.
"I was off the front for a lap but then they caught me," he said.
With 1km to go, Grieve made another move and chased down another rider who had got away up the road "and then just held on in front of the bunch and sprinted that guy for the win".
Fellow John McGlashan student Harrison Chapman claimed bronze in the under-13 boys road race.
The next goal for Grieve is to do well at the under-19 national championships in Timaru next year.
