I have read that "Under all possible proper times between two events, the proper time of the unaccelerated clock is maximal, which is the solution to the twin paradox."
I got that for a clock in it's own inertial frame the proper time is minimal compared to that of other inertial frames, which for me sounds like "moving clocks tick slower". But how do I understand this cited statement? Why is the proper time of an unaccelerated clock maximal compared to accelerated clocks?