Shakyamuni in the early texts taught people to attain arhatship, not buddhahood. In fact, I have not heard or met any early scripture where Gautama advised people to become buddhas. On the other hand, he did say that there isn't much difference between an arhat and a buddha. Now, that's for "Theravada".
In Mahayana there is sudden enlightenment, even buddhahood in this life. For instance, it is a basic point of Zen.
"While teachers of the middle way, mind only, transcendent wisdom, mantra, and other schools may have their own assertions, the fulfillment of those intentions is the same. There is not a single thing that is not contained within mind."
(Gampopa to Düsum Khyenpa, in "The First Karmapa", KTD Pub, p254)
“If you recognize the world of appearance and existence as the mind, realize the mind itself as empty, and have no grasping at the superiority of your realizations — this is the ultimate view."
(Chegom Dzongpa, in "The Book of Kadam", Wisdom Pub, p609)