handle lock happens when you make a sudden stop while the handle is turned almost completely to either side. big bikes weigh more to the front because of the engine placement and when the bike stops suddenly, gravity tends to pull the bike to the ground in the direction where the handle is turned.

it can easily happen if you are at a T-junction, you slowly move forward then suddenly got incoming vehicle from the side that you pull the brake by reaction. because you are not ready to stop, there is a chance for the bike to completely fall over if you are not quick enough to put your leg to the ground. sometimes if the bike is too heavy and it is already leaning over, its probably too late to avoid the fall. you'll risk injuries if you try to hold the bike, better to let it go and hope for minor repair

correct me if i'm wrong.

handle lock is when you turn the handle wayyy too much and start to open the throttle

the bike will lurch to the side, rather than go front as you wanted, and you fall as you tip over. losing balance of a 200+kg bike is very easy.

worse case if you panic, and start to release the clutch while in gear and your hand revs on the throttle. the bike may do unpredictable thing, and in worst case scenario, drag you down with it. luckily, most modern bike has VDS - vehicle down sensor, which cuts off the engine once it's tilted to the side