Yes you can!
There is a famous quote by Henry Ford, "Whether you think you can or think you can't, you are right." Some people find it quite inspirational.

I strongly agree with part of what he said. If you think you can't do something, your limiting beliefs will prevent you from succeeding.
 
I'd like to push on the idea that if you think you can do something, then you will. It takes more than confidence to turn a goal into reality.
 
People act in accordance with their beliefs about themselves. If someone has a poor self-image and lacks confidence to try new things, then it is unlikely that they will get very far in terms of setting ambitious goals and achieving them. Someone with a very strong self-image is more likely to take risks.
 
Our beliefs about our environment, the external forces that surround us, also cause us to act in certain ways. If our understanding of how others perceive us is accurate, then our beliefs can help us gain support to our cause. If we lack a complete understanding and need others to help us, self-confidence alone may not be enough to ensure success.

Misplaced confidence may be viewed by others as arrogance and end up hurting us.
 
Take, for example, a situation where a salesperson is pursuing an opportunity and is highly confident that the customer will buy from them.  If the customer's political environment shifts significantly and the salesperson does not notice, they won't adapt their approach to the new circumstances and may fail as a result.
 
No Guessing!
If you are intent on providing your customer with a solution that truly meets their needs, you need to make sure that you are not guessing about what it takes to help them succeed.
 
Do a reality check.  It can be very useful to get an impartial third-party, such as a coach, to talk through the opportunity and see if you are missing anything.
 
You may find that you are guessing about critical elements, such as:

• The issues your solution must address
• How success will be measured
• Constraints that need to dealt with
• The resources necessary to put the solution in place
• How they are going to decide

 Why guess what the customer is thinking? The best way to find out how accurate your understanding is by asking them directly.
 
As hockey legend Wayne Gretzky said, "You miss 100% of the shots you don't take." If your strong belief that you will succeed is firmly grounded in reality, you can't miss.