The effect on the earliest imbiners of alcohol must be the same as those of modern users - you discover the effect gradually, and experiment to find your own individual level to reach the desired effect. No dount a number of people discovered the effects of alcohol as drinking fermented wines etc. was discovered, rather than just one individual at one time. From that day to this, the feeling of iminent fatality has been an occupational hazard of the intake of alcohol, as people search for that ideal state - being drunk enough to still know what you are saying and doing - but too drunk to really care!