Speed, nothing more is what makes a flip a success.
To quote the great Mickey from Rocky, speed is what we need, we need speed. The first day you purchased that flip was when you made all the money you will make, every day since you are losing more money.
A dollar is not just a dollar.
A dollar is everything you can do with a dollar, this applies to real estate as well as everything else in life. In today's market you can likely earn 10% on your money in any market. Thus if you invested $10,000 into a house (in your personal cash), you are paying $83.34 per month in interest you could be making someplace else, thus you are loosing it in your investment.
Time is not your friend.
Unlike most investments where you earn more the longer you hold it, real estate costs you more (at least in the flip world) the longer you have it. Your goal is to sell quickly, the faster you can sell and make a profit the better off you are.
If you plan to hold your property for three months, every month longer your hold it, you lose, every day earlier you sell it the more you make. The reason is you get the money back out of the investment that will not make any more money and can invest in something that will.
When you purchased your property you thought you would make $5,000 from the flip and your 10% investment. Even as markets continue to rise at the best rates we typically see 6% per year in appreciation, thus every day you do not sell you are earning less than you could in other investments. This remains the same no matter if you were going to make $1 or $10,000 from you initial investment, you already made that money when you purchased the home.
Look at the project as an investment. DO NOT get emotional, you are not going to live there. Make it only as nice as you need to earn the profit you projected, nothing more unless it either increases value or decreases hold time.