The phrase "left to shift for oneself" suggests a situation in which a person is abandoned or left to fend for themselves without any support or assistance. There are several synonyms that can be used to describe this situation, including "abandoned", "isolated", "deserted", "forlorn", "neglected" and "stranded". Each of these words conveys a different nuance or tone, but they all imply a sense of helplessness and vulnerability. When you are left to shift for yourself, it can be challenging to cope with the stresses and demands of life, but it can also lead you to discover your strengths and resilience.