get one's head around sth

get one's head around sth (to be able to understand something)

This idiom is usually used for negative things.

can't get my head around sth /why / how / etc
(not able to understand something difficult or confusing) — никак не могу понять; не могу взять вголову, как/что/почему/проч.~ ума не приложу как / что / почему / проч.

Example: He's tried to explain the rules of the game dozens of times but I just can't get my head around them. (Cambridge Idioms Dictionary)

Example: I've read this document three times and I still don't understand it. I can't get my head around it at all! (ecenglish.com)

Example: I can't get my head around why he bought such a big car. He lives in London—a small car would be better in all the traffic. (ecenglish.com)

Related vocabulary:
(it) [beats me]
Clueless!
not have a clue