I quite often here people say that they never get what they want, or their manifestations aren't working. I believe that one contributing factor in this is that they haven't consciously thought through what would happen if they DID get what they wanted. It may well then be a case that their subconscious mind has thought it through and is throwing up "no, no, don't do it!" messages.
I accept that the following are rather "contrived" scanarios, but let's look at some things that could block you from manifesting:
I want to win the lottery. But if I do, all these people I hardly know will want to be my friends and expect a handout - and I don't want to do that.
A: But if you won even more than you expected, then you could afford to give them something and still have enough for yourself.