I used Sheer Cold on a No Guard Machamp in a battle against my friend and it missed!! What happened?
*The Machamp and my Lapras were both Level 100.
OHKO moves do not fall under that rule (otherwise any Pokemon could guarantee to take Machamp down in one move). They are still only 30% likely to hit.
All other moves will hit Machamp though, including ones like Zap Cannon (only 50% accuracy normally).