This article was originally posted on fortune

That’s the question every wannabe entrepreneur fears the most, but is the most crucial.For those of you ready to take the plunge, I assure you there are few things in life as rewarding. Here are a few of the most important lessons I have picked up along the way:

Be ready for sacrifice

When startups succeed, they do so against all odds. In the beginning, you have nothing except for your own talents and resources. By definition, everyone else is bigger, further along, and more established than you. To win, you have to swim upstream early on–and that requires hard work and long hours. There are no shortcuts.

The first year is the hardest, marked with long days and nights.

No sick days ,No vacations. You have  to get comfortable and adapt quickly to not having a salary for an indefinite amount of time. The specific areas of sacrifice are different for each entrepreneur, but there is always sacrifice of one form or another. Success requires focus, and focus is about trade-offs.

Choose your partners wisely

The ability to evaluate, attract, and build strong working relationships with cofounder(s), early employees, and investors often means the difference between success and failure. Your key early hires will help determine the fate of your business, too.

As a start-up, decide early  that you will value three things above all else:

1) Long-term customer success,

2) Teamwork

3) Getting stuff done.

Hire and promote based on these values, which makes them self-reinforcing. The need for strong partners and employees persists throughout the life of a company, but it is especially important in the beginning.

Obsess over your customer

Many companies talk about customer success, but how many actually put the customer first above all else, always? Obsess over your customer or would-be customer from the very beginning and the rest will work itself out.