4 Mistakes Determined Entrepreneurs Never Make Twice Learn your lesson the first time.

Everybody has goals, but not everybody accomplishes them. Sometimes all it takes is one mistake to derail your progress and jeopardize everything you've worked so hard to achieve.

It is tempting to give up during challenging times. Many people do. But if you have the grit and determination to persevere, you'll find that every mistake contains a valuable lesson that'll make you stronger, more focused and hard to stop -- as long as you don't make the same mistake again.

Related: 5 Lessons You Learn From Your Business Mistakes

Here are four mistakes that determined entrepreneurs never make twice.

1. They always set boundaries.

"No" isn't always an easy word to say, especially to your customers. We live in a world where businesses put their customers on a pedestal. Entrepreneurs learn that "the customer is king." No wonder they feel obligated to indulge unreasonable customer demands. That's why it's important to set boundaries for your customers.

Your unwillingness to tell them "no" will threaten the control you have over your business. You'll lose your focus by making other people's problems your own. Your operation will fall into disarray.

Setting these boundaries is challenging, but it's possible to assert your authority without being disrespectful. Enforce a set of policies within your business and stick to them. Understand that some people will disagree with them, and there will be conflict. When customers challenge your policies, explain why a rule exists. Be honest about the extent to which you're willing to accommodate them. Walk away if they're still unsatisfied. Sometimes it's better to take a short-term loss if it means avoiding a much more complicated set of problems in the future.

2. They never underestimate timelines.

Entrepreneurs are naturally optimistic, and that's great. But, this tendency to be optimistic can result in unrealistic projections about the time it takes to complete specific tasks. This is a psychological phenomenon known as the "planning fallacy." Even though we've done a task a thousand times before, we still underestimate the amount of time it takes to complete it. And this can stop us from organizing our days efficiently and setting realistic deadlines.

That's a problem because deadlines help create expectations. If they're lenient, team members become unmotivated and unproductive. But if they're too tight, people will become stressed and overwhelmed.

Driven entrepreneurs know that even routine tasks contain hidden surprises. That's why they need to manage their time in a way that creates realistic expectations while leaving room for unexpected challenges.

Related: Which Came First: The Time Estimate or the Time-Suck?

3. They don't try to do everything themselves.

You've got a qualified team, yet you complain about how much work you have to get through everyday.

Time is precious. Even if you're the world's biggest workaholic, you've got other interests to pursue in your free time. So why waste away the hours trying to do everything yourself when there are capable people who could do it for you?

Many entrepreneurs are control freaks and terrible at delegating work. They lack trust in other people's abilities, or they think that they're the best person for the job -- and that might be true. But as a business grows, there comes a point where the workload becomes too much for one person handle. During this stage, your most important task as a leader is teaching your team how to think and ask questions for themselves.

You need to set expectations and objectives, but your team members need to be autonomous so that you're not micromanaging them. Failing to delegate will cause your business to stagnate and put unnecessary stress on your shoulders.

4. They avoid making enemies.

Competitors are not your enemies. If you focus all your energy trying to beat them, you'll lose sight of what matters in your business -- making customers happy. Now that doesn't mean you should ignore industry trends and live in a bubble. But you shouldn't develop unhealthy obsessions about constantly getting ahead of people you have set yourself up against as an adversary.

Instead, spend your time identifying what problems your customers need to solve. Develop products and services that they love using, and create experiences that they keep coming back for. If you keep improving your products, logistics and company culture, you'll become a leader in your industry without ruffling any feathers in the process.

Related: 4 Distractions You Must Stop Stressing Over If You Want to Succeed

Mistakes are an unavoidable part of life. But they can cause considerable damage if you don't change the behavior that causes them to re-occur. Learn from your shortcomings, understand your weaknesses, and dedicate yourself to constant improvement. It's the only way you'll solve your problems for good and achieve the determination you need to reach your goals.