Yet thousands of people run a marathon every year.
Don't decide you're unable to run a marathon because 26.2 miles aren't possible tomorrow. But do decide by whether you're able to start a training plan and run 4 miles this week.
The human mind isn't always good at making comparisons. It often tries to compare your present state to the end state without regarding the growth process in between -- it's rather impatient in that regard, often unrealistic too.
The same holds true for that next big thing you've been wanting to try, or build. If your brain expects the finished result impatiently, it may overwhelm you and stop you from starting. The good news is you know this and now you're in control.
You may not be able to create that next big thing right this minute, but you can start the process that moves you toward it gradually and steadily. After all, the surest way to fail is not starting.
A thousand mile journey begins with only one step. Where are you going today?