You have to keep an even keel and trust your inner judgment; a lot of times you may feel like a salmon fighting it's way upstream...You may gain strength from some excellent food on the way or run into some big boulders blocking your ability to go up the next waterfall...but just keep going!
Here is a related and recent quote from Martin Varsavsky, founder of the wireless-sharing company FON, as well as Viatel, Jazztel, and Ya.com (from Bloomberg Businessweek, issue Aug. 30-Sept 5, 2010):
"Arrogance protects you from the naysayers who will try to put your business idea down. You have to say to yourself, 'I believe in what I am doing'. If you listen to everybody, you wouldn't do your idea, because they would tell you about everything that could go wrong with it. I only gave up on one of my seven companies. I made a big mistake because I didn't trust my own judgment. It's about sticking with your crazy idea until it's worth a lot. You put skin in the game, and you fight hard. Sometimes it's borderline madness."
I recently met with a potential client who looked like they had a unique and well thought out new product, with a fairly good working prototype. After reviewing all my available resources, I found out there was a nearly identical product already on the market, with visible signs of intellectual property protection in place.
I then had the unpleasant task of giving my professional opinion to them that it may not be worth it to pursue their idea as the second product to market...Having known firsthand all the trials and tribulations of bringing a new product to market, I advised them to forgo this new product idea and maybe focus their energies on other new product ideas.
I was a naysayer, not of the product idea itself, but of the business proposition of trying to bring a product to market that likely could be jeopardized by infringement in the future...Hopefully, this person has either treated my advice as food or as a boulder blocking the way, and continued on their way upstream...
with their best inner judgment leading the way.