take it upon oneself
to take responsibility for something without being asked; to decide to do sth even though it's not one's responsibility
不经要求就对某事负责; 决定做某事，即使这不是自己的责任
I took it upon myself to write thank-you cards to everyone who came to visit me at the hospital.
我主动给每个来医院看我的人写感谢信。
I took it upon myself to print out these information packets for the meeting.
我自告奋勇把这些会议资料打印出来。
I took it upon myself to count the precise number of children in the audience。
我主动清点观众中孩子的确切数目。
补充解释：
这句短语主要是指一个人很主动，将不是自己分内的事完成了。比如例1，我其实可以不需要写感谢卡，但是我还是主动去做了这件事。再比如例2：这些会议资料本来不是我的事儿，但是我主动去承担了这个打印的任务。
shirk
to avoid doing something that you are supposed to do (work, duty, responsibility)
避免做你应该做的事(工作、任务、责任)
If you shirk your obligations now, you'll definitely regret it later.
如果你现在逃避责任，以后一定会后悔的。
He never shirked from doing his duty.
他从不逃避责任。
If you shirk your responsibilities now, the situation will be much harder to deal with next month.
如果你现在逃避责任，下个月情况就会更加难以处理。
在朋友家吃完晚饭后，我主动把碗筷洗掉了。
I took it upon myself to do the dishes after having dinner at my friend's house.