У-77

БРАТЬСЯ/ВЗЙТЬСЯ ЗА УМ coll VP subj: human more often pfv often infin with пора, надо etc) to become more prudent, begin to act judiciously

X взялся за ум - X came to his senses

X became (grew) sensible (reasonable) X began to act sensibly.

"...Только напоследок хочу сказать тебе: бросай эту канитель, берись за ум, начинай учиться» (Максимов 2). "...But I want to leave one thought with you before you go: quit fooling around. Act sensibly and start studying" (2a).