Failure to analyze the business objectively. Failure to do adequate market research, including getting out into the marketplace and talking to potential customers is asking for trouble. You must decide whether there really is a market for your business. Many an entrepreneur has failed because their projections were far too rosy and not grounded in reality. Being optimistic is great, but not at the expense of sound business judgment.
Lawsuits are legalized war.
And they are a danger to the financial well being of your new start-up. Prosecuting a suit can cost a fortune, as can getting hit with a judgment. Either way, you lose. Justice is all too often not done. I have seen too many outrageously expensive and distracting lawsuits end up with all parties agreeing to drop all actions out of mutual frustration.