comes from 2 Corinthians 1:8-11
"8 We do not want you to be uninformed, brothers and sisters, about the troubles we experienced in the province of Asia. We were under great pressure, far beyond our ability to endure, so that we despaired of life itself. 9 Indeed, we felt we had received the sentence of death. But this happened that we might not rely on ourselves but on God, who raises the dead. 10 He has delivered us from such a deadly peril, and he will deliver us again. On him we have set our hope that he will continue to deliver us, 11 as you help us by your prayers. Then many will give thanks on our behalf for the gracious favor granted us in answer to the prayers of many."

Bad and tough things do happen to godly people... so yes they are part of God's plan for us. However, a big part of that plan is about developing relationships... with God and with each other.

The tough stuff is to teach us to rely on God... and what better way to pursue that reliance but through prayer: "Father, what is going on?... Father, help me, I'm not coping with this... Father, what do you want me to do here?.... Father, help me to trust You.... Father deliver me!"

and as verse 11 says... Prayer helps. Not because God can't act without prayer... but because when we participate through prayer in the work God is doing then we are moved to gratitude and thanksgiving.
God is compassionate for our struggles... He wants others to share that compassion and His means of us doing this is prayer. I pray for your struggle, the I share God's compassion for you and when I see God answer for your good then I give thanks to God for the compassion He shows you.

I also believe prayer motivates us to further actions as the other brothers have said... if a prayer is from the heart it's difficult to just stop at praying when you can act to do something to help. If I'm sincerely praying that God comfort someone in an hour of struggle and then I get the opportunity to go to them and be instrumental in giving that comfort... I'm sure going to take it. This too comes from God's heart I believe.

Blessings
Cat.