Guest post by StartFast Entrepreneur-In-Residence, Kyle Blumin. Follow Kyle on Twitter (@kyleblumin).A funny thing happens when you start a company. All of a sudden everyone and their mother has an opinion as to what you're up to. Everyone from family and friends to advisers and mentors love to bestow their best advice or critique on to you. Your investors won't be shy either. If you let it, this can become cumbersome at best or in some cases debilitating at worst. While they all have great intentions, it is up to you to determine how best to utilize or discard their advice.When starting a company, getting lots of input at the front end of the process can actually help you find the right thing to focus on. In fact, getting more input and learning to sort through it is good up front. Mentor input is feedback that needs to be accepted or rejected based on data. Once you have an executable, market validated strategy laid out, not losing your focus is critical for success. As your company matures, staying on task will be one of your biggest challenges. Your behavior and the actions you take will ultimately lead to your success or failure. You can control a lot about your own behavior. However, there's even more that you can't control about what can impact your business. Ultimately that's why what you focus on is so important.Take the case of Carl Richards. Carl was a financial adviser at Merrill Lynch that ultimately lost his home to foreclosure during the housing run-up and subsequent collapse. While he didn’t create a start-up, his behavior is analogous to my point. The most obvious and easiest decisions can be derailed by losing focus - a financial adviser isn't supposed to lose his house to foreclosure. So how could that possibly happen? Quite frankly, he lost focus by letting the environment around him impact his decisions without focusing on the underlying data. Based upon pure data, he knew that the housing valuations were bogus, yet his behavior got the best of him. It is a refreshingly honest story that you can read about here.There are multiple mission critical decisions that need to be made on a daily basis in the life of a start-up as well as a maturing company. Some decisions need to be made in concert with executing your strategy and others need to be made in order to put out that day's fire. Both of which are important and both can either lever your success or end in dire consequences. Life and death situations happen every day in start-ups and early stage business. Losing focus is not an option - it will kill your venture.Someone once said to me that, "if you live like nobody will, eventually you can live like nobody can." When I was building my companies or executing on strategies to turn them around, I always had options to spend time and energy doing things that seemed like a lot more fun away from the office. I also had options to focus on issues that either weren’t part of the strategy or weren't based on data. I stayed the course with the strategic process and put those non-business related opportunities on the back burner. Sacrifice is part of the game in building your company. It's pretty easy to be taken off course because your buddies are going to Vegas for the week or there are rumors within the marketplace aboutFocusing on driving your business related to data, things that matter and what you can control will go a long way towards driving your success. It’s easier than you think if you refuse to give in to the pressures that are not driven by data. One day that focus will pay off for you. The more you concentrate on it, the easier it is over time. It becomes akin to muscle memory. It should become your best friend.Just keep in mind that the trip to Vegas will be a lot more fun after you’ve succeeded!