The entire basis of personal development rests on your ability to do one single thing: believe in that which you cannot see. We cannot always let what we physically see dominate what we spiritually believe - belief extends beyond the physical.
Let's start with this: global warming is an occurring phenomenon that's invisible to the naked eye. If you went the arctic today, you couldn't see the glaciers melting; you couldn't feel the temperature increase. We know it exists because we look at it from a broader perspective. We look at impacts over time. The fact that we can't actually see it in action does not deter our belief in its existence.
If we cannot clearly see our potential - that is, where we are going and how we will get there - we struggle to believe in it. This requires exploration. This requires a certain belief strong enough to provoke action. Just because we cannot physically perceive something does not mean it is not there. We can't see electricity, but we know its power; we know it can cook a meal, and if untamed, we also know it can cook a man.
If you do not feel smart or attractive or courageous in this moment, it does not mean those things do not exist for you. Not having success right now does not mean success is not coming. You won't always see evidence of these things, but you must still hold belief in them.
Believe in your success, although you may not have it all yet. Know that if you put in the right work, it will happen. There is a recipe to this thing, and should you apply it correctly, success is the only result.
Believe in your ability, although you may not always feel it. Know that you already possess all that you need in order to have it all. It may just be a matter of tapping into something new within yourself.
Believe in lessons learned from failure, whether you can see them or not. This can be difficult. See failure as a clear indication of a flaw in your plan, and an opportunity to move forward by fixing that flaw.
Even if we can't detect a problem day-to-day or implement an immediate solution, we can still solve the problem by taking steps in the present in order to affect the future. That's all self-development is - taking certain steps in the present so as to affect the future. It is making decisions and actions in this moment, so that you may live future moments as you please. You might not recognize what changes need to be made at first, and you may not see the changes immediately, but with the right tools and guidance you are able to solve tomorrow's problems today. We've created energy laws in order to promote current changes for future returns. In the same fashion, you too must make decisions now to create and improve your future - even if it's a future you cannot see clearly.
You cannot let what you see determine what you believe.