To avoid "million dollar disasters," Eidos Montreal decided to keep Thief 4 team at minimal size during the concept stage and until the game's core elements were settled. The team was given free pass to reinvent all and any aspects of the famous stealth FPS series, so they started experimenting. A LOT.
Among other stuff, the team tried out new protagonists, parkour-style environment traversal, third person gameplay and dynamically switching between 1st and 3rd person perspectives. "Concepting was a really cool time," reminisced Steven Gallagher. "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."