Monetizating free-to-play games is a tricky business as veteran developer Peter Molyneux recently discovered.

Previously responsible for the god games Populous and Black & White, along with the Fable role-playing series, Molyneux has now transitioned to mobile development with his studio 22Cans, and he isn’t finding it easy. He initially thought that monetizing his free-to-play iOS mobile-strategy game Godus would be simple, something he now admits was “the biggest mistake I’ve made in the last 20 years.”

It highlights the difficulties that traditional game developers and publishers face in a changing industry, going up against established free-to-play hits like Candy Crush and Clash of Clans.

Speaking at the Apps World Europe conference in London, Molyneux said that monetization was like a drug, reports Develop. He explained that making it seem fair to players in more complex games is a difficult psychological trick, but it’s one developers need to get right.

It “has to be perceived as a fair system,” said Molyneux. “If it’s unfair, those harsh monetization techniques won’t work. Why? Because consumers are starting to say, ‘I’m not going to spend £2 on this because I know if I do, in 20 minutes I’ll have to spend another £2.’”

Molyneux also stressed how much more content Godus players got through compared to 22Cans’ initial expectations.

“I thought they’d take about six weeks to get through that [content],” said Molyneaux. “[It took] six days. It was horrendous. We were looking at the analytics and this graph, and literally hour-by-hour, we were saying to each other, ‘What the hell are we going to do? They are going to run out of content.’”

The most commitment players racked up an average of 12 sessions a day, each between 10 and 40 minutes long. This has put huge pressure on 22Cans to keep adding new content.

“Virtually every three weeks, there needs to be updates,” said Molyneux. “This is just iOS. When we do Android, god knows what’s going to happen. We’ll probably explode from the pressure.”