You might initially think that a higher proof beverage like Scotch would tend to elicit a more consistent personal reaction from one day to another than wine, beer or other more 'delicate', lower proof drinks.
Amongst the many factors that can influence our takes on whisky...
1. Time of day. Try imbibing any particular whisky in the morning and then later on in the day - often two totally different taste experiences. Many (myself included) believe that one's taste buds and perceptual acuity are at their best earlier on during the day.
2. Place. Whether outside in cool, blustery weather or huddled inside beside a fire, location can have a decided influence on how a whisky comes across.
3. Circumstance. A further qualification of No. 2. On one occasion, you may be contemplatively sipping a spirit by yourself. On another, perhaps in a pub with friends/acquaintances. Company, or lack thereof, can make the same drink seem like two entirely different ones.
4. Food. Eating can impart a tremendous impact on how a whisky tastes, whether that whisky is tasted during or soon after feasting.
5. Whatever else you might be drinking - especially when the various beverages you're sampling display radically differing aromatic and flavour characteristics.
As they say, "Variety is the spice of life."