you can't step in the same river twice

baby step

A small effort made towards the completion of a much larger task.

beggars can't be choosers

Something is better than nothing: those who can't provide for themselves should accept whatever help is available.

can't carry a tune in a bucket

Sings very badly.

can't get enough

Greatly enjoys; likes a lot.

can't help

To be unable to avoid a situation, or stop something from happening.

can't stand

cannot put up with

can't stand the sight of

To hate vehemently; to really despise.

can't wait

To eagerly anticipate; to find it hard to wait for a forthcoming pleasurable event.