Entrepreneurship is more about conviction, determination, and will than ideas and market opportunities.

To me, this letter is basically saying you're just not up for the challenge. That's fine -- it's certainly better to admit it now, and it's likely a rational decision.

But the best companies usually aren't created by rational thinkers. The best entrepreneurs can take a horribly broken system and contort it in ways that nobody else even thought of, and then execute on a vision to make it the new reality.

You're not telling your investors "this market is too tough, let's not go here", you're basically just saying "This market really needs to be un-fucked, but I'm not the guy to do it".

Nothing wrong with that, let's tell it how it is.