I have this problem. But not with just games. I tend to leave books lying around, with 10 to 50 to 75 percent read :P

And with this new modern digital era of gaming, I have dozens of games lying around on GOG and Steam that I've barely played or not even tried out... at least yet. It took me about 2 years to finish Witcher 1. I just continued with a pretty late saved game and finished it in a day this January. So I do get some things done, sometime... But despite BG 2 being one of my favorite games of all time I have never finished TOB. I once made it to the final battle... but I did finish the original game about 4 or 5 times.

At some point my interest just drifts away and I put the game or book down, on hold. I might get back to it or not, but I'm not really stressed out about this anymore.

/end rant

I do my best not to worry about it anymore. If I were to force myself to complete games even when I didn't feel like playing them, I feel I wouldn't really be doing the game justice anyhow.

This is not to say that I don't try my best to eventually complete games, I just don't like to feel like I'm on a schedule where I have to play and finish one game before I move on to the next.

If a game really grabs me and I finish it in a week or two, great...if it takes me 24+ years (Phantasy Star 1) to get around to finishing it, that's fine too :)

The only reason I felt those hours on the BG side quest were wasted was because my goal was to play the main quest only.

I do have more games now than I ever have. When I was young, I was lucky if my parents got me two games for birthdays/Christmas. I think I actually beat Splinter Cell four times before I was given another game.

GOG makes it so easy to buy games. They're cheap, and most of them are very good. My wife calls me a snob because I spend days reading reviews and watching gameplay videos before I buy anything. Even on here, I rarely have an impulse buy. I guess I just opened up Steam and felt like I don't finish things anymore. I love video games and it's just sad to me that I have games that are supposed to be masterpieces that I haven't played for more that fifteen minutes.

I do have trouble finishing a game. It all depends on what's going on in my life or how I'm feeling to whether the game frustrates me.

My backlog is backed up with unfinished games. Not too long ago I had finally beaten Silent hill homecoming after shelving it for a couple of years. I got stuck in the sewer with very little ammo and couldn't make it past the enemies. Sometimes I get into funks and not sure if I want to play or finish or whatnot.

Sadly, I start new games when I'm in a funk or if I have trouble with a game, then go back later to try or fail again and making it to the end. Damn, these summer sales have made my backlog HUGE!

Yeah, this is true. Some games are kind of designed to be played in short bursts. Coincidentally im also playing Lost Via Domus and even though it is a bad game, im enjoying it a lot, because i only play one or 2 sections before moving to something else. It just never gets boring that way.

But there are games like Oblivion that i can endure longer gameplay sessions (i did get bored near the end though, and had to force myself to complete it), because there are just so many things to do. I can also take longer sessions in MMOs. Yerterday i played 6 hours of DC Universe Online (according to Steam) and i didnt even notice i had spent so much time.
I feel like every game (or at least most of them) has boring sections that i have to force myself through. Grinding in older JRPGs, for example. Doesnt mean that the game is bad. Same goes for pretty much anything else books, movies, and even songs.

I love games, there are so many, It will take forever and a day to complete half life 2

I'm about to start over on Half Life 2. I don't remember the controls and I'm stuck.

Nobody mentions walkthrough yet to speed up finishing the games, I guess because most gamers will be against the idea of using one, but I personally have no problems with it.

I have no problem at all with walkthroughs. I've found that even with walkthroughs I have trouble with Thief. Walkthroughs for games are great though. I try to only use them if I get stuck though.

My exposure with Thief series is only with Thief: Deadly Shadows. I do not yet own the previous two, so I cannot comment on them. Someday I will probably try them, but for now I can only speak from the experience with the third one in the series.

Anyway, with Thief: Deadly Shadows, I strictly played it in third-person perspective, so in a way it feels rather similar with Splinter Cell series. The reason being I more often than not suffer from motion/simulator sickness associated with first-person perspective, although thankfully it seems that lately I can overcome this a bit. So, maybe, just maybe you have problems with Thief because you are more accustomed with stealth in third-person perspective? Just a guess.