I wish to throw this question out for discussion:
What is the most important thing you know?
We all come from different backgrounds and have had different experiences. Individually we know what we know, but no more.
Collectively we could be pretty smart and achieve more. That is part of the power of a discussion list like the list I moderate ApartmentAssoc or the ones I participate on such as MadisonApartmentOwners, LandlordAssociationOrg or the hundreds of other groups on Yahoo Groups or Google Groups. You ask a question and get an answer.
But what about the question that you do not even know you should ask? So go ahead add what you think is the most important thing you have learned about landlording to the comment section.
[Note I am importing replies from the above Yahoo Groups into this comment section for all to read]