Quote Originally Posted by Antonio1986 View Post
When Russians speaks very difficult to separate between цели and целей.
They sound the same.
Indeed.

Unstressed «ей» is very often pronounced as a simple [и]:
сейчас [с’ич’а́с]
действительно [д’иств’и́т’ил’на]

Different unstressed endings can often sound identical or even be “swallowed” in fast speech so one can distinguish between cases and numbers only by context.