The reason the port took as long as it did, and why we didn’t anticipate the delays, was a combination of several factors.

There were major changes in the tools — both first-party and third-party — between Unity 4 and 5. Some of the third-party tools hadn’t even been updated, and there was nothing to do but wait and pray for this to happen.

There was an enormous amount of work involved in re-lighting, from the ground up, dozens of enormous locations — more work that we’d initially imagined, more work than anyone could possibly imagine. This was partly due to lacking, and overly optimistic, estimates on our part, and partly due to countless bugs in the new lighting system. In addition, with every lighting fix in the biggest scenes, we had to go through an eight-to-twelve hour baking process before we could see the final results. Rinse and repeat, over and over.

We had to rewrite all shaders and scripts to work with the new engine. And we had to deal with a large number of often crippling bugs, some of which persist to this day, requiring desperate workarounds.

Upgrading from one patch or point release to another would fix one serious issue — say, memory leaks — while introducing a completely different issue — such as broken real-time lights. Every new version of the engine would see improvements in one area, and break the game in two, three, ten other areas.

On some days, it was hard to get out of bed and find the will to keep moving forward.

But we did. We did.

The fact that we did is a testament to the team’s commitment, professionalism and loyalty — and to the simple fact that we had no choice. There was no way back. We couldn’t revert the changes. Book Four was almost finished, and it’d been built from the ground up with Unity 5. Starting over was not an option.

We’d come too far. We had to persevere.