Alcohol is virtually poisonous to liver cells and a lot of people traumatise and abuse their livers on a regular basis, usually through drinking alcohol. But the liver is a remarkable organ because, despite this self-inflicted harm, it's very resilient, using its powers of regeneration when necessary.
Not everyone who drinks too much alcohol will develop liver damage. 
It is still unclear why this occurs to certain people but there is some evidence that it could be due in part to a combination of factors including a genetic susceptibility. Consistent heavy drinking can lead to a ‘fatty’ liver in which your liver cells become swollen with excess fat. More seriously it may cause an inflamed liver condition known as alcoholic hepatitis or, ultimately, a permanently scarred and damaged liver – cirrhosis.
Although damaged liver cells are able to repair themselves and the liver can, to a great extent, re-grow itself, there comes a point when the damage becomes irreversible and the normal structure of the liver is lost and replaced with scar tissue (a process called fibrosis).