Of course they can, one way or another. Jesus prayed to "let this cup pass from me" but ultimately "your will be done", and that is how we pray as well.
Or are you just deriding Christianity?
Don't get defensive. It's an honest question, not about Christianity, but about the personal beliefs of the individials who pray. When people (of any religion) get the things they prayed for, they tend to credit the prayer as having influenced the outcome, but when they don't get them, they say "God had a different plan," as if their wishes weren't to be consulted in any case. The two viewpoints seem at odds with each other.