If you like most people, these two words have probably crossed your minds at some point, if not often: I can't. When we face a challenge that seems impossible, we tend to talk ourselves out of trying it. However, it is important for us to avoid talking ourselves into failure before we even give it a try. There are a lot of things that look daunting to us, and they would be if we tried to do them without God. But with Him, all things are possible. When we feel weak and weary, we can remember the words of the prophet Joel: "Let the weak say, I am strong."
What we say matters because it can lead us to believe we can or cannot accomplish something. It is okay to admit that we cannot do something with our human abilities, but we should never doubt God's ability. Upon salvation, we abide in God, and God abides in us. We've been created anew with the supernatural power to do anything God wants us to do. God can do anything through us, even if we feel powerless. 
The next time you feel inadequate and weak, instead of repeating over and over that you can't do it, tell yourself, "I can do all things through Christ which strengtheneth me." (Philippians 4:13 KJV) When God is on our side, nothing can stand against us. He has overcome the world!

Dear Heavenly Father, even when I feel weak or inadequate, please help me to align my words with what You say about me. I am strong, I am able, and I am loved. Remind me of this daily so that I can live to my full potential and nothing can hold me back. No matter what challenges I face, give me strength as I choose to follow Your lead. Let the Holy Spirit flow through me as I abide in You. 
In Jesus's name I pray. Amen.