My DH is in big law, transitioned over after a decade in government.
He was brought in as a partner-track counsel. He negotiated a guaranteed bonus for 2 years, with the idea that by the 3rd year he would be doing well. By the second year he realized that the firm was not a good fit for him and left to another firm.
He is still at the other firm, and started developing a good group of his own clients within 2 years, made equity partner his 3rd year because he had a solid book of business.
So you get a couple of years of runway to build a book of business but then if you don’t, they will likely let you go. Or you become a service partner if another partner has enough work, but that’s becoming less common becasue they don’t have to make you partner (or at least an equity partner - they might meet you as an income partner).
My DH is pretty focused about all parts of his job - he cares a lot about doing good legal work (at the point it’s making sure his team produces amazing work), being super responsive to clients, pitching new clients, and paying attention to all his clients. He also cares a lot about getting bills out on time and managing client budgets. Being a successful partner is only partly about being a good lawyer.