Prayer is asking God for something you want. Sure, it could be thanking Him, or praising Him, or talking to Him in general, but the basic premise of prayer is to gain something you want.
There are many beliefs about how prayer works. Claiming that you need to have enough faith is a convenient back-door rationalization to explain away why you didn't get what you ask for.
Here is why this one is B.S.: Imagine the "Creator" of all things sitting on His throne in heaven. He hears a request from a mother to save her child from a life-threatening disease. God considers the faith of the requestor....oh...too bad....one mustard seed short of enough faith. Sorry, the child has to die.
Scenario 2: An 8 year old girl asks for a pony. It's hardly possible to have more faith than a child. They haven't lived long enough to know any better. So God sees the request come through, and sees it needs to be approved due to the pure faith of the requester.
Does that seem reasonable? I don't think so either. So let's just rule out the whole faith-based argument.
Another rationalizations for prayer failing: It's not God's will.
So if it IS God's will, it will be done and there is no need to ask. If it's NOT, then asking does no good.
Maybe if enough people with strong enough faith all ask for one thing, God will "change His plans" and grant it. I guess we can rule this out, since millions have been praying for world peace since day 1, and it's never been granted.
ScenariosPrayer: "God, please watch over me on my trip, and see that I arrive safely."
God: "hmm....well....I WAS planning on you dying in a horrible crash, but since you asked nicely, I guess we can avoid that. Good thing you asked! ;)"
Prayer: "God, please let me win the lottery."
God: "The Faith is strong with you! Curse you! Must....grant.....wish....."
Prayer:"God! WHY? Why did you let my dog get hit by a car?"
God: "Cut me some slack, how did I know you didn't want that to happen? You never asked Me to protect your dog. Besides, I can't be bothered with such trivial matters unless your faith is at level 27, minimum."
I hope the above scenarios highlight the ridiculousness of prayer.
If you claim that prayer is simply good for mental health....like meditation...I'll buy that, but that's all it could be good for, unless you believe in the type of God I portrayed in the above scenarios.