I think I picked up a misconception from Jonathan Edwards (rightly or wrongly understood) that faith is only believing that God will do what God has promised to do. The point was, don’t believe that God will do something he has not promised to do – that’s presumption, not faith.
But now I think that you also have to believe that God will probably do what God has said he’ll probably do. For example, Matthew 7:7-11 says that God gives good things to those who ask him. It doesn’t say he’ll give you any specific good thing every time you ask, so it’s not a promise that God will do something in particular. Based on my view before, then, there was no room for faith here – you just say, I have no idea whether God will answer or not.
But the Biblical attitude needs to be, “wow, God gives good gifts! So he’s very likely to answer this prayer” as long as it’s a reasonable one.
There’s a lot more intricacies here, but this simple truth is one I need to start with for now.