It's easy to miss a payment, get behind on something or just have something pop up you had no idea about now days.
When I was buying my first house shortly after getting married you would not believe all the sh*t that showed up on my wife's credit which was now OUR credit.

She had no less than 4 collection totaling around 8K. I managed to to to each collection agency, give them the story of what happened 50% truth; and get them to agree in writing to remove it from the reporting agency since I was paying it in full.
I had one house payment that was short about 2 years ago because of my escrow fund was short and my payments were set up auto pay so I never saw the increase notification and it got missed. Luckily they removed the missed payment since I pointed out I had been paying extra for years and was actually ahead of my due payment schedule by 2 or 3 payments. If you dont stay on top of those things they can bite you in the azz later.
You have to be careful about things such as to many lines of credit open also even if they are all paid on time or even paid 100% each month. To many or especially to many large lines of credit can be bad. Also even to many inquiries can hurt your score and you dont even have to OK the inquiry sometimes. It can be a per say soft inquiry because someone wants you to sign up for some card or line of credit but it still shows up.
I'm sure with a little work I could close some lines of credit and clean things up more to get up to 800 but???