I tend to agree as well. Some say the entry is least important but I don't see how this could be. If your entry is good, you're not taking much heat, and if you are, then this tells you right away the trade isn't working so you can get out.
As for the edge discussion, I agree as well, but I'm not sure if what you say is specific enough for me. So many things have to work together. The OP might actually have very good trades, but horrible trade management. If perhaps all he does is move his stop or target, maybe he would be profitable. So this could be one edge. The other edge might be that he isn't taking each trade that he wants to because of fear, perhaps fear from the previous loss. That could be another edge he isn't exploiting.
But all of this to me doesn't really mean edge in terms of "if you do this, you will make money". The "this" is a combination of probably 10 things. If you take any one of those things away, there won't be profitability. On their own, each of these things won't get you past the finish line. I've seen over and over that one of the biggest edges that traders have is experience which allows them to discriminate between trades. There might be little nuances that prevent them from taking a trade, maybe something based on another market they watch at the same time.
Anyway, so I guess what I'm saying is that even though you say you need one good thing, I'm not sure what this one good thing can be because if all the other parts don't line up, this one good thing will appear like a loser. Precise criteria for trade entry can I think be very very good, but without applying this at a key level, or perhaps at a key time, or perhaps in conjunction with the general trend of the day, etc., would mean this trade entry might lead to more losses than profits. Anyway.. just thinking out loud.
Edit: Opps, I think I combined your post along with the post of lawrence-lugar in my reply.