Shemuel wanted to establish the calendar for the Exiles on his own, but Rabbi Simlai's father didn't allow him because he didn't know the "secret of adding [to the calendar]": Rosh HaShanah 20b
Unable to convice Rabbi Yochanan to teach him Sefer HaYuchasim [Book of Lineages], although he was a very quick-learning Torah Scholar: Pesachim 62b
