on (one's) shoulders
One's own responsibility or obligation. My siblings' care has been on my shoulders ever since our parents died.
*on someone's shoulders
Fig. on someone's own self. (*Typically: be ~; carry something ~; fall ~; have something ~; leave something ~; put something ~.) Why should all the responsibility fall on my shoulders? She carries a tremendous amount of responsibility on her shoulders.
on one's shoulders
As one's responsibility, as in The king carries his entire country on his shoulders, or The success of the conference rests on Nancy's shoulders. This metaphoric use of shoulders as the burden-bearing part of the body dates from the late 1300s.
on somebody’s ˈshoulders
if blame, guilt, etc. is on somebody’s shoulders, they must take responsibility for it: I feel like all the responsibility is on my shoulders, which is quite stressful.