Lets do the math : you can minimize issues with tenants and buildings through good management, but you will always have a (hopefully small) percentage of tenants/buildings with problems.
The more doors you own, the more problems you will have. It boils down to simple math. fewer doors=fewer problems.
Pipes leak, furnaces die, tenants stop paying rent. It happens.
Also, some investments are more management intensive than others by their very nature, like rooming houses and student rentals. Some markets are as well, like low income towns vs downtown big city.
The key is finding a balance between the benefits you want (income for me!) and the type of investing you do. There are many ways to skin a cat in this business, and number of doors shouldn't be your only yardstick to measure your success. What are your goals? High income? Net worth? Retirement? Taylor your strategy to achieve your goals.
I know real estate investors holding only one door (their house!) that have huge incomes and tons of net worth as note holders and hard money lenders.
