to investigate thoroughly; to examine closely; to probe into; to get to the bottom of
to be obsessed with a thought; to brood over; to worry about
問題の本質を突き詰めた。
I got to the bottom of the problem.
彼は一つの哲学を突き詰めている。
He is probing deeply into a single philosophy.
原因を突き詰めると人的ミスに行き着いた。
When I investigated the cause thoroughly, it came down to human error.