You press the power button on your pc, you log into your account and launch Steam.
You browse your game library and find all kinds of second guesses, games you put only a couple of hours into and games that didn't live up to their expectations.
You now find yourself with nearly 100 games, majority that probably won't see a second install.
IF you could go back in time, which games would you of purchased and which games wouldn't you have in order to keep that "perfect" list.
Mine to keep would be,
Elderscrolls Skyrim
Fallout 4
Alien Isolation
Natural Selection 2
CSGO
Shogun 2
Project Cars
The rest I would probably delete, feel free to upload a screenshot of your steam library, I would probably do the same when I get home from work.