I think the only wrinkle is how to quantify level of intoxication for driving and other things that have inhibition restrictions.

You get the idea.Of course, you want to maximize your potential rental rate, but always quantify that to see if it makes sense. 

But I always tell people to quantify “significant” because for one person that could be $2K and for another it could be $20K.

Risk is much harder to quantify as a number, but if goals are being met and your risk is low, who cares if you're sacrificing opportunity? 

Gary Keller, in his book Millionaire Real Estate Investor, recommends that approach, with regular refinancing to twenty five- to thirty percent down, fifteen year loans, because that is the way to get best interest rate, and achieve strong long term returns.The last, and perhaps most important point is harder to make, because it is very hard to quantify, but it has to due with risk.

I can quantify repair costs averages, rent increases, turnover, etc. but you can't control utilities.

Quantify your situation:30k in debt and can be debt-free in 5 years.

Victoria, BC (6.7) and Toronto (6.5) are the next least affordable housing markets in Canada.It has even become an issue in our current federal election with the Prime Minister pledging resources to quantify the effect of foreign capital on housing in Vancouver and Toronto.

Rent income is $1200 or can even do $1250 if i upgrade kictchen with backslash and stainless appliances. am not sure how to quantify vacancy but overal possible cash flow around $350 monthly, take 1 month out for vacancy and year cash flow maybe be $3000. not accounting for taxes, depreciation and equity built.

I think what both of you are saying is that likelihood (or probability) is less when you are not leveraged (fewer units) , The impact could be more severe than if you leveraged and owned more units Let me quantify Basis From example above $300K start with $50 K houses / Rent $750 Expenses (%50) $375 ( you still have taxes and insurance regardless if you carry a mortgage or not) Appreciation 5% Option 1 Buy 6 $50K houses free and clear Starting equity = (300K value – 0 Loan Balance) = 300K Income = $750 Expenses (%50) $375 Cash Flow $375 Times 6 units = 2250 Month (same as Mr Duncan Demo) Option 2 Buy 12 $50K houses ($25K Down, $25K Financed) Starting equity = (600K value – 300K Loan Balance) = 300K Income = $750 Expenses (%50) $375 P&I (25K at %5 for 30 years yields monthly payment of $134 Cash Flow $240 Times 12 units =$ 2880 Month Risk assessment / Management While the probability of getting a bad tenant is more with the greater # of units, The IMPACT would be less: Risk Analysis Hazard : getting a bad tenant that late/skips on rent Effect: you lose one months rent ($750) Probability of Incidence (PofI) = in our example 1 in 20 (5%) Option 1 PofI = 6 units *(.05) = 30% chance Impact + (-$750 cash flow ) -> Net cash goes from $2250 to (2250-750) $1500 a (%33) decrease Option 2 PofI - 12 units * .05 = %60 chance you get stuck Impact = ((-$750) cash flow -> net cash goes from $2880 to (2880 – 750) 2130 = 26% decrease So while the chance Is greater with multiple units , the impact is lessoned due to the other income streams.