A Regret List will help you avoid them

Once we've learn to accept that mistakes are inevitable, we can get on with the business of avoiding them. The sooner the better.
In fact, you can even do one better: Regret your mistakes even before you do them. This concept comes from a little known Asian proverb which translates roughly as "to regret before doing is wise,  to regret after is futile."
So how do you regret your mistakes before you do them?
This is an exercise that can be done as part of Step5 or even Step3 and Step4. It is best done in a group because it benefits from a deep pool of experience. There will be reservations when done within this setting as trust will be a core issue. Exercise your judgment on this. Doing it alone may require you to do some soul searching as well as analysis.
Begin by putting everybody into the mindset of having solved the problem. Restate the problem as in Step2 as having solved them and addressed the primary goals. Think happy thoughts. Then ask everyone of what they would have done differently or done better.  You can also start with statements like "I wish I hadn't forgot to...".  It may be awkward for some people but ask them to think of it like going through a list of things they would have normally done after closing the door of the apartment or house as they were leaving it.  This when we would try to think whether we forgot something or left something behind before we go too far.

Have one person taking notes as the ideas and statements can come quickly and from many people at once as they share their experiences and thoughts.  Once this is done you are left with a list of things to remember as well as to avoid. This could turned into a checklist at the end of the solution implementation. Or it could inform specific issues or people. 
When doing this as part of Step3 and Step4, use the list to inform the process. We can use it to define desirable solution traits. Parts of it can be added to the solution definition itself to narrow down possible solutions. Finally, the list can be used as a basis of a selection criteria to choose the solution to be implemented.
In the end, it would help us avoid foreseeable mistakes or even change our solution for the better.