Do you believe anything that you want to accomplish is possible?
It's a simple question, but it's far from simple to answer! In fact, I expect that if you're a thoughtful person, you can immediately think of many things that you would love to accomplish, but sincerely doubt that they're actually achievable.
I have good news—and bad news for you...
The good news is that you REALLY CAN achieve anything that you can imagine! Yes, you really, really can! Don't doubt it!
The bad news is that if you DO doubt it—you're right! You won't be able to do it!
There are two reasons that I can make such a statement. The first is that if you study the peak performance, motivational, self-help experts, you will discover that they have been saying these things for many years—with LOTS of examples of people who have achieved extraordinary things though ordinary means.
The historical and anecdotal evidence of what people can accomplish when they really focus on something is astounding. Edison, NASA (in the 60's—not today), the Wright Brothers, George Washington Carver, and many, many others achieved extraordinary results and succeeded in doing what many had said were "impossible" goals.
But there is a better source for making such a statement: God himself.
It is amazing how simple God makes most things (simple for us, that is—the things that God himself made were far from 'simple'—such as you). And yet we tend to stumble over the simplicity.
Jesus said, "I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him." — Mark 11:23
Was Jesus lying to us? Was he trying to trick us into saying something absurd, and then laughing at us for being stupid enough to try? Absolutely not! He starts out the statement saying, "I tell you the TRUTH..."
The problem is—we don't believe him!
In Matthew 21:22 Jesus said, "If you believe, you will receive whatever you ask for in prayer."
In Mark 9:23 Jesus said, "Everything is possible for him who believes."
In Genesis 11:6 God said, "If as one people speaking the same language they have begun to do this, then nothing they plan to do will be impossible for them."
If you are a Christian, then you already believed John 8:24 where Jesus said, "Therefore I said to you that you will die in your sins; for if you do not believe that I am He, you will die in your sins." You believed, confessed, and were saved (see Rom 10:9-10). If you believed Jesus' words about salvation and who he is, why are his words about faith and belief any different?
Part of the difficulty is that salvation was instantaneous—but not everything done by faith is instantaneous. So when we step out in "faith" and don't see immediate evidence that what we have said will happen, we start second guessing ourselves or (even worse) confessing failure. Part of faith is holding fast.
When Jesus spoke to the fig tree in Mark 11, it was not until the next day that the disciples saw evidence that what Jesus said had come to pass, so be patient!
If you believe you will succeed, your mouth will speak accordingly. If you believe you will fail, your words will also give you away, for "out of the abundance of the heart, the mouth speaks."
Do you wonder if you really can accomplish anything? Go spend some time studying what God has said on the subject. Trust that he's not lying. Believe...then go achieve!