Eidos Montreal's Thief team has explained a number of reasons for the game's prolonged pre-production stretch.
The next-gen sequel - which was officially revealed for the first time on Tuesday - is said to have been in the making for almost five years, and was kept away from the public eye since its original May 2009 announcement.
The main cause of the extended development stretch, the developer told Game Informer, is that in order to avoid "million dollar disasters", the Thief team was kept small and within the concept stage of development until a clear idea emerged.
Given free rein to reinvent the Thief series, the Eidos Montreal team experimented with a brand new character and even experimented with a third-person title with environment clambering, similar to gameplay in Assassin's Creed.
At one point in development, GI reveals, the game had so many third-to-first-person transitions that the constant camera shifting was making people nauseous.
Narrative director Steven Gallagher said: "Concepting was a really cool time. There were a lot of ideas. It was very creatively energetic, but there was a lot of stuff that went on the table and was quickly taken off the table, and then placed in a dark room never to be seen.
"Some of the early concept stuff had Garrett a little too soft in his approach. That was a fine line to walk. I had a lot of problems with some of the early focus tests because I had turned his movements up too much towards the female spectrum."
A year ago the studio hired Splinter Cell veteran Stephane Roy as producer, in an attempt to bring focus to the project.His job was to "figure out the original mandate" of the project and avoid any confusion caused by the team's years of experimentation.
"I noticed that when I asked several directors about the original mandate, there was no clear answer," he explained. "When you try a lot of things, sometimes it's difficult to keep the focus.
"You try this and you try that and you forget what the game is about. It happened a couple of times where we were wrong, and that was tough on the team, but at the end of the day, people on the game really believe in Thief."
Eidos Montreal's experimentation helped the studio settle on what it now believes is the formula for designing a great stealth game, says GI: "Force players into a series of impossible situations and then give them the tools to escape."
Hit the link for more Thief 4 gameplay details via Game Informer.