I’ve referred to it often enough that I will transcribe it here, with apologies to its original author. I did search to attribute it properly, but could not discover the author’s identity. If you happen to know that person’s identity, please comment and I’ll add attribution.
The mountain is enormous. It will take a long time to climb and there is no guarantee that, even if you set out to conquer it, you will ever succeed. Dwell on this and you will soon conclude that you probably ought to leave that mountain well alone. The mountain though, must be tackled. You know this. You feel it, strongly and instinctively. So you had better stop talking yourself out of the task and start talking yourself into it. Believe what you want provided you convince yourself that your journey is possible.