Long-term is very difficult to predict and ever-changing, especially in these times.  

Out of state investing can certainly be difficult off the bat but can definitely be much more rewarding. 

DTI had become my hurdle, making regular plain vanilla mortgages difficult.

Concessions are also somewhat difficult to comprehend, since real estate can be a game of telephone, sometimes the transaction is just better off, without attempting to get four parties to understand the numbers. 

Re-habing a house from scratch is very difficult, we are doing it by ourselves which is even more difficult but enjoying the process and learning.

$1,250,000 all in is often difficult these days!

If I were to refinance (which would be impossible as you stated), it would be even more difficult to cash flow. 

I find it extremely difficult to give letter grades to an area.

I have a difficult tenant with section8 houston housing.

@Sam Booth - I agree that planning out your CapEx can be difficult.