do you mean "why do lifters go bad"?
Well over reeving an engine can kill a lifter. Its a ticking that sticks around usually in between a certain rpm and load.
Some times lifters can gum up and prevent a check ball from seating. this is usually apparent when the lifter makes constant noise of noise just when the engine is cold. A fix for this is using a detergent of some sort like ATF or Sea Foam.
I'm no expert but this has been my findings. good luck.
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