I realize cap is based on the seller's most optimistic assumptions, so lots of due diligence is necessary.

Warren Buffet says to "buy from pessimists and sell to optimists."

I'm pretty open and honest, and I'm still young, naive, and optimistic. 

There are exceptions, but generally speaking, you will spend a lot of time to gain no equity and likely end up break even with a bunch of used furniture in an optimistic scenario in my honest opinion.

So, I'd say the 50% rule is too optimistic for your property, or that you've underpriced the rent, or that you're paying expenses you shouldn't.

We'll see how this one goes very optimistic though

I am personally not optimistic about much appreciation in the coming period.

"Any ship but a partnership"(per my Dad, after dealing with several real estate  partners during the 1980's RE crash) Will the partnership that starts so optimistically when it looks like profits will be made still hold together when it is clear that losses will be taken?

There are exceptions - no one is always right, and sometimes you're more optimistic than you should be - but having a hard handle on costs is going to make or break you as a rehabber. 

I'm very optimistic that I'm going to gain a lot of knowledge through this site that's going to help me in my future investments!