The flight from tradition began with Martin Luther (1483-1546) who rejection of the "sale of Indulgences".
What is an indulgence? An indulgence is the remission of some or all temporal punishment due to sin. This is accomplished by definite prayers, visiting a particular holy place or doing some prescribed good work. Indulgence did not take away sin, only a priest in Confession could do so.
At this time Pope Julius II granted indulgences to those who contributed to the building of St. Peter's Basilica in Rome. It was similar to paying a fine for breaking the law instead of spending time in Jail. This concept probably originated in the early Church belief that one who died for the faith, a martyr, had his sins forgiven along with all temporal punishment. Luther probably did not oppose indulgences per se, rather the abuse of them by those exaggerating its power e.g. making believe that indulgences forgave sins.
But Luther had another problem, disbelief that the Church had the power to forgive sin. In his view, only faith in Jesus Christ could forgive sin. He held on to the Sacraments Baptism and Eucharist. He insisted that the Eucharist represented the real presence of Christ and he, as an ordained priest, still had the power of changing bread and wine into the body and blood of Christ. But, for how long? He believed in the priesthood of the faithful but not the priesthood as a sacrament. As a result, Lutherans still believe in the real presence of Christ despite the fact that they no longer have a valid priesthood. The Eucharistic Sacrifice can only have a symbolical significance and Lutherans can experience a spiritual communion with Christ because Christ can give grace to whomever he wills. In other words, in their celebration of the Mass, the bread and wine are not changed into the body and blood of Christ.
In the final analysis, Luther looked to the Bible as the only source of faith. There was no visible Church established by God in which man can work out his salvation. Man is saved from sin only by believing that Christ will forgive his sins which included full pardon for the penalties due to sin. The dogma of Purgatory was rejected. (newadvent.org)/Catholic encyclopedia: Martin Luther, by Ganss)
Luther's views were adopted by many because the invention of the printing press made possible the dissemination of Scripture. In the beginning of Christianity there was no written New Testament. Later, the Bible was copied by hand and was very expensive; only Churches and the rich could afford to purchase one. Add to this the inability of many people to read and Luther would not have been able to influenced many people.