The definition of insanity is doing the same thing over and over again and expecting different results.
The real story
No evidence exists that Einstein ever said or wrote this. The earliest known appearance is from October 1981, at an Al-Anon meeting reported in a Knoxville, Tennessee newspaper. A Narcotics Anonymous pamphlet repeated it in November 1981. The phrase emerged from anonymous twelve-step recovery communities, not from Einstein. The comprehensive reference work "The Ultimate Quotable Einstein" explicitly lists it as misattributed.