If you want to understand someone, you need to build up a friendship with him/her, how to do it? Of course, it depends on different people, but... at least you need to spend time to him/her, share to each other, let him/her know yourself, listen to his/her sharing, keep in touch...etc. When you know him/her more, sometime, you can understand more his/her thinking or mindset, and what things he/she like or he/she doesn't like.

It's same with our relationship with our Heavenly Father, do I spend time to Him? Do I share to Him? Do I listen to Him? Do I understand Him? If not, how can I say I know this is from God, and this is God's will or this is God's plan... etc. We need to spend time to Him, build up a good and close relationship with Him, otherwise it's hard to understand Him.

Our Heavenly Father is our God, our Lord, and also our Best Friend in our life.