You just get back to your best after a long lay-off with injury. You find your spot in the team, and everything looks to be going great.
Then, bang. One tackle, and your body - as well as your world - is turned upside down.
You can't help but feel sorry for Adam Matthews as he stares at three months out with a shoulder injury.
I don't believe there was any malice in the tackle from Keith Lasley, and it has to be remembered it was the landing rather than the contact that caused the damage.
But, it was the kind of challenge which we are told is not permitted in today's game, even if was commonplace in my time as a player.
None of which will matter to Adam as he begins his recovery from surgery then starts his rehab.
He was out for months with a hamstring which ended last season prematurely for him.
This lay-off will be even more frustrating because he immediately misses huge games, including the double-header against Ajax.
It's a big blow to the club because he was looking very effective in right midfield.
But, that's why Celtic have a squad, and James Forrest's return couldn't be better timed.