From a profitability perspective, I do a lot of things right - high nutritional quality, low cost feed from a local mill, hatching my own so as to not pay replacement costs, feed supplementation via low maintenance varied pasturage to further bend the feed curve. Deep litter method to produce useful compost for my gardening.
I do a lot of things wrong, too. I'm not using "production" breeds, so my yields relative to my inputs are lower than they could be. My coops have gone thru several costly iterations as they've been expanded or redesigned for my needs and climate. I don't cull frequently enough (adding to my "carry costs"). I added rabbits - produce more (and superior) compost faster, quicker to breed, quicker to produce meat protein with the trade of no eggs - but higher feed costs, and higher upfront housing costs (which I redid). I have pekin ducks (NOT cost effective), I have goats (which I need, desperately, to cull to manageable numbers). and a day job to pay for it all.
Also, I'm in an economically depressed area of the country which produces a lot of chickens - I could break even at best, excluding my labor, and accounting for the value of all the outputs (including that glorious compost).
So the one useful thing I'll offer from my example is to FOCUS. Even if you are brilliant, try to do too much, too fast, and you will find a lot of things getting away from you. That, and "you will make mistakes - they are costly learning experiences. But more costly if you don't". One a purely economic basis, most will find their margins to be very narrow.