This is the 107th most frequent Slovak word.
musí
"Musí" means "must" or "has to" in English.
In this sentence, 'musí' conveys a strong assumption about the subject's state (being tired) based on contextual evidence.
Musí byť unavený po takej dlhej ceste.
He must be tired after such a long journey.
'Musí' here is employed to denote a general requirement or rule applied to all individuals within the subject group (everyone).
Každý musí urobiť domácu úlohu.
Everyone must do their homework.
Here, 'musí' is used to express a necessity or obligation for the subject (he) to perform a specific action (going to the store).