Historians have debated this question for some time. The consensus for many years after the revolution emphasized the tightly-knit organization of the Bolsheviks. According to this interpretation, the Bolsheviks managed to topple the Russian provisional government with relatively little support from the Russian people as a whole. Lenin, in short, was the leader of a cadre of revolutionaries who, unified in purpose, were able to overcome his opponents, a mixture of royalists, moderate socialists, and republicans who lacked the same will and cohesion that characterized the Bolshevik movement.
While not discounting the importance of these factors, modern historians tend to emphasize the degree to which Bolshevik ideology and popular appeals resonated with the Russian people. The Bolsheviks were especially popular in St. Petersburg, where the people gradually became convinced that only they could be trusted to bring the disastrous war to an end. This interpretation also places great importance on the dire conditions that confronted the Russian people in 1917. Bread and fuel shortages, exacerbated by the war itself, made them willing to embrace Bolshevik reforms. In fact, the Bolshevik program of "peace, land, and bread" was in many ways a response to the demands of the Russian people, especially soldiers and sailors and their families in Petrograd.
In short, the success of the Bolshevik Revolution in 1917 can be attributed to, among other factors, their organization, the conditions faced by the Russian people, and the inability of the provisional government to deal with these conditions.