Take action
I see a lot folks spend a significant amount of time posting/writing/talking about real estate investing. I agree that continuing education and planning are critical to success.
With that said, the single biggest mistake most investors make is not making a mistake. People are worried about failing, so they don't give themselves an opportunity to succeed.
The same can be said about life in general. As kids, we care so little about what others think. We follow our passions and do what we love. As we become adults, we lose that sense of freedom and lack of inhibition. Here's an example - any of us that have kids (I have 3 sons) watched them learn to walk. They tried and failed, and tried and failed, and we continued to encourage them. At what point did we say, "Hey, you're not very good at walking, so quit trying. Move on to something else." Never!
As adults, we tend to follow the opposite approach. If you make a mistake or screw something up as an adult, what's the first thing you think? Most people think, "Boy I hope no one saw that!". When you look at it from that perspective, who is smarter? The "adult" or the 8 month old refusing to quit until (s)he can walk like a pro.
"What if I lose money?" you say. Let me take the suspense out of it for you. You will lose money in your life as an investor - real estate or otherwise - I guarantee it. Now that you know failure is a part of the deal, shouldn't it be easier to take action? If it goes bad, so what? Take the standing 8 count, get back in the ring and keep fighting. Also - If you are in this solely to make money, find something else to do. If you don't love it, you won't go after it with everything you have, and you won't be successful.
I'm an executive in the food business as well as a seasoned real estate investor. When people ask me how I got to where I am at, I tell them "I tried. When someone asked for a volunteer to take on a hard project, I raised my hand and took action." It wasn't preordained I would be successful. I made myself successful - mostly by screwing up so much stuff that I learned very quickly how things can go wrong. I used those lessons to change my actions and deliver more desirable outcomes. One of my favorite sayings is "Experience is something you get right after you needed it." I have a ton of "experience".
Moral of the story - take action. Make mistakes. Tony Robbins is quoted as saying "There is no success or failure - there are only outcomes. If you don't like the outcome from your actions, take different actions". Words to live by for all of us in every aspect of our lives.