I have questions regarding expected value.

If you make more +ev decisions than negative ones your suppose to make a profit it in the long run. At least that's the theory right so poker in a way can be played perfectly and their is a certain way it should be played which is finding good ev spots. But the only way to recognize your in a good ev spot is to have a read on your opponent for an example I was in a limped pot with qj the flop gives me up and down straight draw with two overs I'm check raised all in after much confusion I elect to call he flips over aces and played them passively preflop causing me to completely eliminate that hand in his range in the first place. now I'm left drawing and I blank. So my question is with out a read or narrowing down a range of hands you can't know if your plus ev right or no? Can you say something is plus ev with out a read and how do you no if it is plus ev and your making the right moves? Do you just run possible ranges to your current holding on equity softwares and if your holding is higher equity compared to their range your makeing a plus ev decision.

Thanks for the help.