Who hasn't thrown or given away some wardrobe item only to regret it 2, 5, 10 or 20 years later?
To avoid the 2-year regret: box it, bag it, store it for two years. If you haven't hauled it out after two years, it was indeed past its date of usefulness. Some things just don't "wear" well. It may be that piece you bought out of desperation and the immediate need. It was okay for the occasion but you hardly ever looked at it again. It might be the uber-fashionable thing that lit up your life briefly but sputtered out quickly.
If regret sets in after 5 years, you are probably fondly remembering a piece that in reality may have been worn (as in worn out) or was just ahead of its (fashion) time. For the latter just congratulate yourself on your foresight and rest assured there was no way you could know chunky tunics would be in style this fall.
If it was in your closet 10 years ago chances are it would indeed be cut differently today. Ten- years-ago tweed pants are not today's pair. The waist! The leg! The length! Not to mention the fact that your body might not be the one you had ten years ago.
20 years plus should be the Land of No Regrets. The pussy cat bow blouse you had in 1980 is not the same blouse you might buy today. For one thing you will probably buy silk today rather than Banlon, Orlon or Virgin Acrylic. The armholes will be cut differently, the bow will have a different flair, the color will be decidedly less garish. It will in fact be a different blouse. Perhaps you have a giant, walk-into attic and don't actually get rid of anything, just banish it upstairs. That doesn't mean you can wear it again and call it "vintage". Old clothes on old ladies are just old. Ouch.