From this early article on Tamoxifen.
https://www.nature.com/articles/s41416-023-02158-5
"Reductions in recurrence after about 10 years of follow-up were 21%, 29% and 47% for 1, 2 and 5 years of treatment, respectively. The corresponding mortality reductions were 12%, 17% and 26%, respectively, with a significantly significant test for trends in both recurrence and mortality."

The quote refers to early breast cancer. You might be one of the lucky ones who don't get a recurrence, even though you don't take tamoxifen. But I, personally, would not call it a success story--which implies that you could control the outcome--just a lucky roll of the dice.