Why is it hard to believe in these beings for you?
I'm not sure how to explain it exactly. I've never really had spiritual experiences. Religion has largely been an intellectual pursuit for me, with bodily discipline (fasting, etc.) thrown in because I know it is beneficial. But actual experiences I am short on. I think I've had one in my life, and that wasn't anything lofty or great, it was just the feeling that there was something other around. Even my belief in God is largely intellectual, which is one reason that I was probably prone to fall into disbelief. I'm not sure what to say beyond that. I just have a hard time believing in these invisible beings flying around, planting thoughts in my head or trying to get me react a certain way. I mean, I believe on a purely intellectual level that there is such a being as the devil, but in practice in my daily life I have a hard time accepting all the extra doctrines and practices having to do with the demons.
I know how you feel. I admit, I'm the same way, which is why I have a tendency to attack whatever contemporary miracles people talk about, some that are so far-fetched. I remember Steve Harvey making a joke about people's "testimonies:"
"Lord, I bought something from a store...and Lord, I didn't like the dress, and Lord Jesus, thank you, I had the receipt, and Lord, Jesus I was able to return the dress with full refund, praise the Lord, Alleluia!"
To which Steve answered, "That ain't no miracle; that's a store policy!"
That's how I feel when I here some of the bizarre testimonies of fellow Christians on what they experienced, from things that are coincidences to bizarre Narnia-like experiences.
To answer your question though, I notice a difference between when I pray a lot to times when I don't pray. I get a sense of peace and comfort in prayer, and I am able to combat my weaknesses better. Truly, experience does help in my belief, that faith is something to be experienced. I've never met an angel or a demon, not even a saint (except maybe my grandfather in my dreams), but I feel weaker spiritually without prayer. I try to think that I'm consubstantial with them, since we are two natures in one, angelic and animalistic, which helps a little, i.e. that part of me is what I see around me and part of me is the intellectual self-awareness, something that cannot be seen, which what angels and demons are.
But I don't believe that everything that I am tempted with come from demons. Could be a tendency of my own, a thorn in my flesh that I must battle, like the tendency to intellectualize things.
But I'm sure God Who understands your and my weaknesses in this issue would be more than happy if you and I continue to pray and live a life of repentance even when having trouble believing in the angels that help us and the demons that cause strife, dare I say the former (prayer and repentance) more important than the latter (belief in angels and demons).