Lennie's physical strength is his worst enemy.from Of Mice and Men Do you agree? If not, why?

I, too, disagree with this statement.  As lynnebh
notes, Lennie's problem is his mental weakness, which prevents him from understanding
his own strength and learning how to control it. 

In many
regards, Lennie's physical strength is an asset.  Because Lennie is virtually incapable
of answering questions for himself, George, when the two apply for jobs, points
out Lennie's physical strength to prospective employers.  Because the work of
ranch-hands consists of manual labor, Lennie's strength helps him to do his job
well. 

Never in the novel does Lennie seek to harm another
person or animal.  He accidentally kills the puppy, he hurts Curley in self-defense and
only after George gives him permission to fight back, and he accidentally snaps Curley's
wife's neck when he becomes panicked by her screaming. 

So
while it may seem that Lennie's strength causes harm to others, readers to evaluate the
novel closely will understand that Lennie's mental limitations get him into trouble, not
his strength.