
All it accomplishes is getting the person doing it killed or incarcerated, and giving the state a free excuse for further repression. An adventurist is someone who thinks that doing revolutionary actions prematurely will inspire and activate more people to follow, when the historical record does not show that to be true.
It was primarily used by Vladimir Lenin and revolutionaries inspired by him to criticize the revolutionary-minded people around them who did random disorganized attacks before building deep support among the population and coordination with a larger organization. Basically Lenin saying “you can’t spark the revolution before you have revolutionary numbers on your side”